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In sheep infected with bovine leukemia virus (BLV), transcription of structural, enzymatic, and accessory genes is silenced. However, the BLV provirus transcribes a series of non-coding RNAs that remain undetected by the host immune response. Specifically, three RNAs (AS1-L, AS1-S, and AS2) are consistently expressed from the antisense strand, originating from transcriptional initiation at the 3'-Long Terminal Repeat (LTR). To investigate the role of these non-coding RNAs in viral replication and pathogenesis, a reverse genetics approach was devised, capitalizing on a mechanistic disparity in transcription initiation between the 5' and 3' promoters. A two-nucleotide mutation (GG>TA) in the TFIIB-recognition element (BRE) impaired antisense transcription originating from the 3'-LTR. In the context of the provirus, this 2bp mutation significantly diminished the expression of antisense RNAs, while not notably affecting sense transcription. When inoculated to sheep, the mutated provirus was infectious but exhibited reduced replication levels, shedding light on the role of antisense transcription in vivo. In comparison to lymphoid organs in sheep infected with a wild-type (WT) provirus, the mutant demonstrated alterations in both the spatial distribution and rates of cell proliferation in the lymph nodes and the spleen. Analysis through RNA sequencing and RT-qPCR unveiled an upregulation of the Hmcn1/hemicentin-1 gene in B-lymphocytes from sheep infected with the mutated provirus. Further examination via confocal microscopy and immunohistochemistry revealed an increase in the amount of hemicentin-1 protein encoded by Hmcn1 in peripheral blood mononuclear cells (PBMCs) and lymphoid organs of sheep infected with the mutant. RNA interference targeting Hmcn1 expression impacted the migration of ovine kidney (OVK) cells in vitro. In contrast to the WT, the mutated provirus showed reduced oncogenicity when inoculated into sheep. Collectively, this study underscores the essential role of antisense transcription in BLV replication and pathogenicity. These findings may offer valuable insights into understanding the relevance of antisense transcription in the context of human T-cell leukemia virus (HTLV-1). Author summary: In sheep infected with bovine leukemia virus (BLV), the transcription of genes encoding viral proteins is silenced. However, the virus constitutively produces long non-coding RNAs from the opposite strand of the integrated genome. To comprehend their role, we used reverse genetics to alter the BLV sequence, reducing the production of these antisense RNAs. When inoculated to sheep, this modified virus was infectious but could not replicate as well. Compared to the original strain, the number of mutated viruses was reduced in the peripheral blood and the lymphoid organs. Gene expression in B-cells from sheep infected with the mutated virus was altered, particularly affecting the Hmcn1 gene, which is involved in cell migration. Importantly, the modified virus did not cause leukemia in sheep, indicating the involvement of antisense RNAs in effective cancer development. In summary, our study underscores the significance of these antisense RNAs in the ability of the virus to replicate and induce illness. This understanding may offer insights into similar mechanisms in viruses affecting humans such as HTLV-1. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effect of bovine leukemia virus (BLV) on the systemic profile of naturally infected dairy heifers during the transition period. Pregnant Holstein and Jersey heifers (n=24) were distributed in pairs into two experimental groups: (BLV+) and (BLV–). Animals in the BLV+ group were divided into two subgroups based on the median BLV proviral load (high and low). The animals were then assessed at weeks –3, –2, –1, calving time (0), +1, +2, and +3. Blood samples were obtained for hematological and biochemical analyses, as well as haptoglobin measurements. Farm BLV screening revealed a herd BLV prevalence of 57.25% and heifer BLV prevalence of 38.7%. Mean corpuscular hemoglobin concentration was the only hematological variable for which group interaction was observed, with BLV+ cattle having higher values (33.29 ± 3.39%) than BLV– cattle (31.08 ± 2.31%). Aspartate aminotransferase activity was higher in the BLV+ heifers. The BLV+ group had greater incidence of inflammation (haptoglobin ≥ 2.0 mg/dL). Fibrinogen concentrations were also higher at weeks 0 and +1 in BLV+ heifers than in BLV– heifers. A high proviral load affected total leukocyte and lymphocyte count; however, this profile was not observed in the low proviral load and paired BLV– heifers. To our knowledge, this is the first study to report the impact of BLV infection on the health of dairy heifers during the transition period, demonstrating the effect of proviral load on white blood cell changes and early inflammation in infected animals. [ABSTRACT FROM AUTHOR]

Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis, an oncogenic deltaretrovirus that has emerged as a potential zoonotic infection. The BLV naturally infects cattle and causes economic losses through a slow persistent infection with various clinical symtoms following preleukosis. The main objective of this study was to determine the seroprevalence of BLV antibodies in cattle and buffaloes in the border provinces of the Eastern Anatolia region, Türkiye, using the agar gel immunodiffusion (AGID) assay and enzyme-linked immunosorbent assay (ELISA). For this purpose, a total of 1,033 serum samples were collected from 982 cattle and 51 buffaloes from the provinces of Ağrı (n = 178), Iğdır (n = 252), Kars (n = 317), Van (n = 221), and Hakkari (n = 65) during 2021 - 2022. In AGID and ELISA tests, seropositivity for BLV-specific antibodies was not detected in cattle and buffaloes from the mentioned provinces. This study revealed that BLV was not circulating in cattle and buffaloes in the easternmost border provinces of Türkiye during the sampling period and contributed to determine the status of BLV in the mentioned region. Due to the presence of virus in other regions of Türkiye and neighboring countries, Iran and Iraq, it is recommended to control animal movements, continue efforts to combat the transmission of the virus, and maintain control measures. [ABSTRACT FROM AUTHOR]

The list of standard abbreviations for JDS is available at adsa.org/jds-abbreviations-24. Nonstandard abbreviations are available in the Notes. Endemic infectious diseases remain a major challenge for dairy producers worldwide. For effective disease control programs, up-to-date prevalence estimates are of utmost importance. The objective of this study was to estimate the herd-level prevalence of bovine leukemia virus (BLV), Salmonella enterica ssp. enterica serovar Dublin (Salmonella Dublin), and Neospora caninum in dairy herds in Alberta, Canada, using a serial cross-sectional study design. Bulk tank milk samples from all Alberta dairy farms were collected 4 times, in December 2021 (n = 489), April 2022 (n = 487), July 2022 (n = 487), and October 2022 (n = 480), and tested for antibodies against BLV, Salmonella Dublin, and N. caninum using ELISA. Herd-level apparent prevalence was calculated as positive herds divided by total tested herds at each time point. A mixed-effect modified Poisson regression model was employed to assess the association of prevalence with region, herd size, herd type, and type of milking system. Apparent prevalence of BLV was 89.4%, 88.7%, 86.9%, and 86.9% in December, April, July, and October, respectively, whereas for Salmonella Dublin apparent prevalence was 11.2%, 6.6%, 8.6%, and 8.5%, and for N. caninum apparent prevalence was 18.2%, 7.4%, 7.8%, and 15.0%. For BLV, Salmonella Dublin, and N. caninum , a total of 91.7%, 15.6%, and 28.1% of herds, respectively, were positive at least once, whereas 82.5%, 3.6%, and 3.0% of herds were ELISA positive at all 4 times. Compared with the north region, central Alberta had a high prevalence (prevalence ratio [PR] = 1.13) of BLV antibody-positive herds, whereas south Alberta had a high prevalence (PR = 2.56) of herds positive for Salmonella Dublin antibodies. Furthermore, central (PR = 0.52) and south regions (PR = 0.46) had low prevalence of N. caninum -positive herds compared with the north. Hutterite colony herds were more frequently BLV positive (PR = 1.13) but less frequently N. caninum -positive (PR = 0.47). Large herds (>7,200 L/d milk delivered ∼>250 cows) were 1.1 times more often BLV positive, whereas small herds (≤3,600 L/d milk delivered ∼≤125 cows) were 3.2 times more often N. caninum positive. For Salmonella Dublin, Hutterite colony herds were less frequently (PR = 0.07) positive than non-colony herds only in medium and large strata but not in small stratum. Moreover, larger herds were more frequently (PR = 2.20) Salmonella Dublin-positive than smaller herds only in non-colony stratum but not in colony stratum. Moreover, N. caninum prevalence was 1.6 times higher on farms with conventional milking systems compared with farms with an automated milking system. These results provide up-to-date information of the prevalence of these infections that will inform investigations of within-herd prevalence of these infections and help in devising evidence-based disease control strategies. [ABSTRACT FROM AUTHOR]

The current literature has identified many abnormalities in the immune expression of cows infected with the bovine leukemia virus (BLV). These studies have focused on individual cell, gene, or protein expression, failing to provide a comprehensive understanding of the changes in immune expression in animals with BLV. To identify the overall alterations in immune expression during BLV infection, the transcriptomes of the peripheral blood mononuclear cells (PBMCs) of cows seropositive or seronegative for BLV antibodies were sequenced. Whole blood samples were collected from 20 dairy cows and screened for BLV antibodies and PCR was used to quantify the proviral load of the samples. PBMCs were separated from whole blood using density gradient centrifugation from which RNA was isolated and sequenced. Three seropositive samples (BLV+; n = 3), including one of each PVL category, low (n = 1), moderate (n = 1), and high (n = 1), and three seronegative samples (BLV−; n = 3) were sequenced for differential gene expression analysis. The results showed major differences in the transcriptome profiles of the BLV+ and BLV− PBMCs and revealed a wide variety of immunological pathways affected by BLV infection. Our results suggest that disease state and PBMC gene expression vary depending on BLV proviral load levels and that BLV causes the suppression of normal immune responses and influences B and T cell gene expression, resulting in immune dysfunction. [ABSTRACT FROM AUTHOR]

Background and Aim: Bovine interleukin 15 (bIL15) is a potential immunotherapy that can block the spread of bovine leukemia virus (BLV). However, immune checkpoints that maintain body homeostasis may reduce their effectiveness. Thus, an analysis of the effectiveness of bIL15 while blocking negative immune regulators is necessary. We aimed to obtain recombinant bIL15 (rbIL15) and determine its percentage using monoclonal antibodies against bovine cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed cell death ligand 1 (PD-L1). To achieve this goal, peripheral blood mononuclear cells (PBMCs) from healthy and BLV+ cattle were treated with bIL15 using a CTLA-4– and PD-L1–blocking algorithm. Materials and Methods: The codon-optimized bIL15 gene was synthesized under de novo conditions using polymerase chain reaction (PCR). The synthesized gene was cloned into pET28 and transformed into electrocompetent Escherichia coli BL21 cells; rbIL15 was purified using metal affinity chromatography and analyzed using sodium dodecyl-sulfate– polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting. The expression of the Bcl2, STAT3, and STAT5 genes was studied using qualitative PCR. An enzyme-linked immunosorbent assay (ELISA) was used to analyze interferon (IFN)-γ production by rbIL15-treated mononuclear cells. Results: Analysis of rbIL15 using SDS-PAGE and western blotting revealed a specific product weighing 24 kDa. The optimal conditions for rbIL15 induction were 0.2 mM isopropyl-β-D-1-galactopyranoside and 37°C. When rbIL15 was added to PBMCs from healthy cattle, the Bcl2, STAT3, and STAT5 genes were expressed. ELISA of the culture medium of rbIL15-treated PBMCs revealed IFN-γ production. When PBMCs from healthy cows were treated with rbIL15, CTLA-4, and PD-L1 blockade together, they did not produce more IFN-γ than the rbIL15 group. Using PBMCs from BLV+ cattle, combination treatment increased IFN-γ production. Conclusion: The biological activity of rbIL15 is characterized by the induction of transcription factors and the production of IFN-γ. Using rbIL15 with CTLA-4 and PD-L1 blockade in PBMCs from healthy and BLV+ cows led to the production of a transcription factor and cytokine. The results demonstrate the possibility of using this method to improve immunity and immunological memory in patients with chronic viral infections. [ABSTRACT FROM AUTHOR]

Enzootic bovine leukosis, a neoplastic disease caused by the bovine leukemia virus (BLV), was the primary cancer affecting cattle in China before 1985. Although its prevalence decreased significantly between 1986 and 2000, enzootic bovine leukosis has been re-emerging since 2000. This re-emergence has been largely overlooked, possibly due to the latent nature of BLV infection or the perceived lack of sufficient evidence. This study investigated the molecular epidemiology of BLV infections in dairy cattle in Henan province, Central China. Blood samples from 668 dairy cattle across nine farms were tested using nested polymerase chain reaction assays targeting the partial envelope (env) gene (gp51 fragment). Twenty-three samples tested positive (animal-level prevalence of 3.4%; 95% confidence interval: 2.2, 5.1). The full-length env gene sequences from these positive samples were obtained and phylogenetically analyzed, along with previously reported sequences from the GenBank database. The sequences from positive samples were clustered into four genotypes (1, 4, 6, and 7). The geographical annotation of the maximum clade credibility trees suggested that the two genotype 1 strains in Henan might have originated from Japan, while the genotype 7 strain is likely to have originated from Moldova. Subsequent Bayesian stochastic search variable selection analysis further indicated a strong geographical association between the Henan strains and Japan, as well as Moldova. The estimated substitution rate for the env gene ranged from 4.39 × 10−4 to 2.38 × 10−3 substitutions per site per year. Additionally, codons 291, 326, 385, and 480 were identified as positively selected sites, potentially associated with membrane fusion, epitope peptide vaccine design, and transmembrane signal transduction. These findings contribute to the broader understanding of BLV epidemiology in Chinese dairy cattle and highlight the need for measures to mitigate further BLV transmission within and between cattle herds in China. [ABSTRACT FROM AUTHOR]

A 5-year-old Japanese Black cow presented with astasia. Bovine leukemia virus (BLV) was detected in the peripheral blood with lower proviral load (PVL). No enlargement of surface lymph nodes or lymphocytosis was observed. Necropsy revealed no enlarged lymph nodes in the thoracic, abdominal, or pelvic cavity. Spinal epidural and peri-medullary adipose tissue was increased in the spinal canal of lumbar to sacral vertebrae, Histopathological examination revealed tumor invasion of the epidural adipose tissue, and a diagnosis of B-cell lymphoma was made. The PVL in tumor tissue was higher, and monoclonal integration of BLV was confirmed. It was a rare case of bovine enzootic leukosis that formed a solitary mass around the spinal cord which might cause hindlimb paresis. [ABSTRACT FROM AUTHOR]

Background and Aim: Bovine interleukin 15 (bIL15) is a potential immunotherapy that can block the spread of bovine leukemia virus (BLV). However, immune checkpoints that maintain body homeostasis may reduce their effectiveness. Thus, an analysis of the effectiveness of bIL15 while blocking negative immune regulators is necessary. We aimed to obtain recombinant bIL15 (rbIL15) and determine its percentage using monoclonal antibodies against bovine cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed cell death ligand 1 (PD-L1). To achieve this goal, peripheral blood mononuclear cells (PBMCs) from healthy and BLV+ cattle were treated with bIL15 using a CTLA-4– and PD-L1–blocking algorithm. Materials and Methods: The codon-optimized bIL15 gene was synthesized under de novo conditions using polymerase chain reaction (PCR). The synthesized gene was cloned into pET28 and transformed into electrocompetent Escherichia coli BL21 cells; rbIL15 was purified using metal affinity chromatography and analyzed using sodium dodecyl-sulfate– polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting. The expression of the Bcl2, STAT3, and STAT5 genes was studied using qualitative PCR. An enzyme-linked immunosorbent assay (ELISA) was used to analyze interferon (IFN)-γ production by rbIL15-treated mononuclear cells. Results: Analysis of rbIL15 using SDS-PAGE and western blotting revealed a specific product weighing 24 kDa. The optimal conditions for rbIL15 induction were 0.2 mM isopropyl-β-D-1-galactopyranoside and 37°C. When rbIL15 was added to PBMCs from healthy cattle, the Bcl2, STAT3, and STAT5 genes were expressed. ELISA of the culture medium of rbIL15-treated PBMCs revealed IFN-γ production. When PBMCs from healthy cows were treated with rbIL15, CTLA-4, and PD-L1 blockade together, they did not produce more IFN-γ than the rbIL15 group. Using PBMCs from BLV+ cattle, combination treatment increased IFN-γ production. Conclusion: The biological activity of rbIL15 is characterized by the induction of transcription factors and the production of IFN-γ. Using rbIL15 with CTLA-4 and PD-L1 blockade in PBMCs from healthy and BLV+ cows led to the production of a transcription factor and cytokine. The results demonstrate the possibility of using this method to improve immunity and immunological memory in patients with chronic viral infections.

Background and Aim: In the Caribbean region of Colombia, the concomitance of endemic infectious agents is a common problem, and coinfections are possible, increasing the complexity of cattle herds’ sanitary, reproductive, and productive problems. This study aimed to estimate the seroprevalence of bovine leukemia virus and its association with bovine infectious abortion in grazing Creole breeds from tropical herds in the Colombian Caribbean. Materials and Methods: For the determination of bovine leukemia virus (BLV), bovine viral diarrhea virus (BVDV), bovine herpes virus-1 (BoHV-1), and Neospora Caninum (NC), the enzyme-linked immunosorbent assay technique was used. Matrix analysis was performed to represent multiple seroprevalence in the same cow. To explore the association between the seroprevalence of BLV and bovine infectious abortion agents, a multivariate logistic regression model was used. Results: The seroprevalence was as follows: BLV 30.78%, BVDV 33.01%, BoHV-1 12.85%, and NC 8.96%. In the multivariate logistic regression model, seroprevalence of BVDV (OR 10.8; 95% CI: 7.5–15.6) and seroprevalence of BoHV-1 (OR 1.8; 95% CI: 1.1–3.0) were associated with the seroprevalence of BLV. Conclusion: Animals infected with BLV are more susceptible to coinfections with BVDV and BoHV-1. Implementing healthy measures against these two immunosuppressive infections could enhance the hygiene of numerous cattle herds. This study was designed as a retrospective cross-sectional study, which limits the ability to confirm that BLV is the primary infection. Further studies to confirm the primary infection of BLV with an active viral coinfection are necessary and the factors associated with these phenomena.

Background and Aim: In chronic viral infections, cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and programmed death ligand 1 (PD-L1) significantly suppress immune responses. The CTLA-4 receptor abundance in regulatory T cells showed a positive association with viral load and a negative association with interferon-gamma (IFN-γ) production in bovine leukemia virus (BLV)-infected cattle. Blocking this receptor boosted IFN-γ production, recovering immune response against this illness. In human cancer patients, not everyone responded positively to non-immunotherapy using CTLA-4 receptor antibodies. The present study analyzed the synergistic effects of CTLA-4 and PD-L1 receptor blockade on IFN-γ production in BLV+ cattle in vitro. Materials and Methods: The genes for bovine CTLA-4 and PD-L1 were artificially produced. The amino acid sequences of the extracellular receptor domains were sourced from the National Center for Biotechnology Information PubMed database. The western blotting and liquid chromatography with tandem mass spectrometry (LC-MS/MS) techniques were employed for the characterization of recombinant CTLA-4 (rCTLA-4) and recombinant PD-L1 (rPD-L1) proteins. The immunoinhibitory effects of recombinant proteins in Staphylococcus enterotoxin B (SEB)-stimulated cattle peripheral blood mononuclear cells (PBMCs) were investigated. Enzyme-linked immunosorbent assay (ELISA) was used to analyze monoclonal antibodies against rCTLA-4 and rPD-L1. Antibodies generated from peripheral blood mononuclear cells of healthy and BLV-seropositive cows were employed to evaluate their blocking capabilities. Results: The resulting recombinant proteins specifically reacted with commercial homogeneous monoclonal antibodies (mAbs) using ELISA and anti-His-tag mAbs using western blotting. Analysis of the proteins using LC-MS/MS revealed correspondence with the sequences of rCTLA-4 and rPD-L1 located in the Mascot database. rCTLA-4 and rPD-L1 proteins inhibited IFN-γ production in bovine PBMCs of activated SEB. When PBMCs from cows were cultured with activated SEB containing rCTLA-4 and rPD-L1, the mAbs increased IFN-γ production in PBMCs. The combined cultivation of mAbs and PBMCs from BLV+ cattle enhanced IFN-γ production in the cells. Conclusion: These findings suggest that the combined blockade of bovine CTLA-4 and PD-L1 receptors can be used as a therapy for bovine leukemia. However, it was shown that a single PBMC sample from a BLV-positive donor did not amplify the synergistic effect. Therefore, it is necessary to perform further studies on a larger population and assessing a wider range of cytokines.

ABSTRACT: We investigated the prevalence and spatial distribution of selected pathogens associated with infectious diseases of dairy cattle in Ontario, Canada. The cross-sectional study surveyed bulk tank milk for antibodies against bovine leukemia virus (BLV), Mycobacterium avium ssp. paratuberculosis (MAP), and Salmonella Dublin, and for the presence of mastitis pathogens (Staphylococcus aureus, Streptococcus agalactiae, Mycoplasma bovis). Between October 2021 and June 2022, bulk tank milk samples were obtained from every commercial dairy farm in Ontario (n = 3,286). Samples underwent ELISA testing for the presence of BLV, MAP, and S. Dublin antibodies, and quantitative PCR testing for the detection of specific antigens of pathogens associated with mastitis. Bayesian models were used to estimate prevalence, and spatial analysis was carried out to identify regional clusters of high pathogen prevalence. Prevalence varied for different pathogens, and BLV was widespread across dairy farms in Ontario, with an estimated prevalence of 88.3%. The prevalence of MAP, Staph. aureus and S. Dublin in Ontario dairy herds was 39.8%, 31.5%, and 5.1%, respectively. The vast majority of dairy herds in Ontario were free of intramammary infections caused by Strep. agalactiae and M. bovis. Clusters of increased positive test rates were detected for S. Dublin, MAP, and Staph. aureus, indicating potential geographic risk factors for pathogen transmission. For S. Dublin, an area of increased test positivity rates was detected in southwestern Ontario, close to the Canada-United States border where most of the dairy herds in Ontario are located. Conversely, a localized cluster of positive test outcomes involving 14 subdivisions located in the southeastern region of Ontario was detected for Staph. aureus. Findings from our survey highlight the importance of the testing of aggregated samples and conducting spatial analysis as part of disease surveillance programs, and for implementing risk-based trading approaches among dairy producers.

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis and causes a persistent infection that can leave cattle with no symptoms. Many countries have been able to successfully eradicate BLV through improved detection and management methods. However, with the increasing novel molecular detection methods there have been few efforts to standardize these results at global scale. This study aimed to determine the interlaboratory accuracy and agreement of 11 molecular tests in detecting BLV. Each qPCR/ddPCR method varied by target gene, primer design, DNA input and chemistries. DNA samples were extracted from blood of BLV-seropositive cattle and lyophilized to grant a better preservation during shipping to all participants around the globe. Twenty nine out of 44 samples were correctly identified by the 11 labs and all methods exhibited a diagnostic sensitivity between 74 and 100%. Agreement amongst different assays was linked to BLV copy numbers present in samples and the characteristics of each assay (i.e., BLV target sequence). Finally, the mean correlation value for all assays was within the range of strong correlation. This study highlights the importance of continuous need for standardization and harmonization amongst assays and the different participants. The results underscore the need of an international calibrator to estimate the efficiency (standard curve) of the different assays and improve quantitation accuracy. Additionally, this will inform future participants about the variability associated with emerging chemistries, methods, and technologies used to study BLV. Altogether, by improving tests performance worldwide it will positively aid in the eradication efforts. [ABSTRACT FROM AUTHOR]

Background and Aim: In the Caribbean region of Colombia, the concomitance of endemic infectious agents is a common problem, and coinfections are possible, increasing the complexity of cattle herds' sanitary, reproductive, and productive problems. This study aimed to estimate the seroprevalence of bovine leukemia virus and its association with bovine infectious abortion in grazing Creole breeds from tropical herds in the Colombian Caribbean. Materials and Methods: For the determination of bovine leukemia virus (BLV), bovine viral diarrhea virus (BVDV), bovine herpes virus-1 (BoHV-1), and Neospora Caninum (NC), the enzyme-linked immunosorbent assay technique was used. Matrix analysis was performed to represent multiple seroprevalence in the same cow. To explore the association between the seroprevalence of BLV and bovine infectious abortion agents, a multivariate logistic regression model was used. Results: The seroprevalence was as follows: BLV 30.78%, BVDV 33.01%, BoHV-1 12.85%, and NC 8.96%. In the multivariate logistic regression model, seroprevalence of BVDV (OR 10.8; 95% CI: 7.5-15.6) and seroprevalence of BoHV-1 (OR 1.8; 95% CI: 1.1-3.0) were associated with the seroprevalence of BLV. Conclusion: Animals infected with BLV are more susceptible to coinfections with BVDV and BoHV-1. Implementing healthy measures against these two immunosuppressive infections could enhance the hygiene of numerous cattle herds. This study was designed as a retrospective cross-sectional study, which limits the ability to confirm that BLV is the primary infection. Further studies to confirm the primary infection of BLV with an active viral coinfection are necessary and the factors associated with these phenomena. [ABSTRACT FROM AUTHOR]

Background and Aim: In chronic viral infections, cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and programmed death ligand 1 (PD-L1) significantly suppress immune responses. The CTLA-4 receptor abundance in regulatory T cells showed a positive association with viral load and a negative association with interferon-gamma (IFN-γ) production in bovine leukemia virus (BLV)-infected cattle. Blocking this receptor boosted IFN-γ production, recovering immune response against this illness. In human cancer patients, not everyone responded positively to non-immunotherapy using CTLA-4 receptor antibodies. The present study analyzed the synergistic effects of CTLA-4 and PD-L1 receptor blockade on IFN-γ production in BLV+ cattle in vitro. Materials and Methods: The genes for bovine CTLA-4 and PD-L1 were artificially produced. The amino acid sequences of the extracellular receptor domains were sourced from the National Center for Biotechnology Information PubMed database. The western blotting and liquid chromatography with tandem mass spectrometry (LC-MS/MS) techniques were employed for the characterization of recombinant CTLA-4 (rCTLA-4) and recombinant PD-L1 (rPD-L1) proteins. The immunoinhibitory effects of recombinant proteins in Staphylococcus enterotoxin B (SEB)-stimulated cattle peripheral blood mononuclear cells (PBMCs) were investigated. Enzyme-linked immunosorbent assay (ELISA) was used to analyze monoclonal antibodies against rCTLA-4 and rPD-L1. Antibodies generated from peripheral blood mononuclear cells of healthy and BLV-seropositive cows were employed to evaluate their blocking capabilities. Results: The resulting recombinant proteins specifically reacted with commercial homogeneous monoclonal antibodies (mAbs) using ELISA and anti-His-tag mAbs using western blotting. Analysis of the proteins using LC-MS/MS revealed correspondence with the sequences of rCTLA-4 and rPD-L1 located in the Mascot database. rCTLA-4 and rPD-L1 proteins inhibited IFN-γ production in bovine PBMCs of activated SEB. When PBMCs from cows were cultured with activated SEB containing rCTLA-4 and rPD-L1, the mAbs increased IFN-γ production in PBMCs. The combined cultivation of mAbs and PBMCs from BLV+ cattle enhanced IFN-γ production in the cells. Conclusion: These findings suggest that the combined blockade of bovine CTLA-4 and PD-L1 receptors can be used as a therapy for bovine leukemia. However, it was shown that a single PBMC sample from a BLV-positive donor did not amplify the synergistic effect. Therefore, it is necessary to perform further studies on a larger population and assessing a wider range of cytokines. [ABSTRACT FROM AUTHOR]

The list of standard abbreviations for JDS is available at adsa.org/jds-abbreviations-24. Nonstandard abbreviations are available in the Notes. Bovine leukosis is prevalent in the North American dairy industry, and its effect on animal health and production is widely documented. However, not all bovine leukemia virus (BLV)–infected animals transmit the virus equally. Animals with high proviral loads (HPL) of BLV are associated with higher transmission risks, and therefore, their removal may reduce transmission and eventually within-herd prevalence. We aimed to evaluate the impact of selectively removing HPL cows on the within-herd BLV prevalence and incidence rate of BLV infection in 10 dairy herds. Annual blood or milk samples (or both) were collected from adult cows over 3 yr. Positivity with BLV were determined by ELISA tests, and proviral loads in blood of BLV-positive animals were estimated with BLV SS1 quantitative PCR assays. Herd managers were encouraged to consider the proviral load when making culling decisions and implement BLV control practices. Cows with high proviral load had the highest relative risk of removal, indicating the farmers prioritized HPL cows for culling. The within-herd BLV prevalence decreased significantly in 4 herds, whereas BLV incidence rate decreased in 9 herds. Over the 3 yr, the proviral load demonstrated a relatively stable level, suggesting a single proviral load test in an adult cow may suffice to make culling decisions. [ABSTRACT FROM AUTHOR]

The bovine leukemia virus (BLV) is an important infectious agent transmitted from cattle to humans. It is considered one of the oncogenic viruses in breast cancer, so an accurate detection of this virus is important. The study aimed to design a specific and sensitive method based on TaqMan® real-time polymerase chain reaction (RT-PCR) for BLV detection. Probes and primers were designed using bioinformatics software for a 108 pairs region of the BLV tax gene. Criteria employed for determining analytical sensitivity were prepared using in-vitro RNA transcriptions. The National Center for Biotechnology Information (NCBI), basic local alignment search tool (BLAST) databases various viral panels and genomic samples from healthy individuals (Qom Province, Iran in 2023) were used to verify analytical specificity and clinical specificity, respectively. This method can measure a minimum of 10 copies of DNA and RNA mL-1. Moreover, the assay is linear in the range of 100 - 109 copies mL-1. By testing negative specimens, the method specificity was 100%. The reproducibility results of the reaction were examined at the intra- and inter-assay comparison. In fact, 10 technical replicates of each concentration of the control sample were analyzed in each working reaction. Due to the locally made kit, exact sensitivity and specificity, rapid analysis, and relatively low cost, as compared to commercial kits of other countries, the method introduced in the present study could be suitable for accurate detection of the BLV. Also, the TaqMan® real-time PCR method could be detected in cattle and human and before malignant changes of breast cancer which could reduce infection and breast cancer. [ABSTRACT FROM AUTHOR]

Bovine leukemia virus (BLV) establishes a lifelong persistent infection in dairy cattle. White blood cell count (WBC) is correlated with proviral load in the blood and milk of BLV-infected cattle, and testing WBC can be used to assess both BLV infectiousness levels and risk of BLV transmission from different types of infected animals. The objective of the study was to compare effective transmission rates (β) and the basic reproduction ratio (Ro) among two types of BLV-infected dairy cows in Chile: those affected with persistent lymphocytosis (PL) vs. aleukemic (AL). The estimated (β) coefficient was higher in PL cattle [1.1; 95% Confidence interval (CI) (-1.6, 3.8)], compared to AL cattle (-3.1; 95% CI = -3.7, -2.5). In addition, the Ro was higher in PL cattle (60.4; 95% CI = 3.5; 820.6), compared to AL cattle (1.5; 95% CI = 0.7, 3.1). The ratio between PL/AL expected rate of cases was 73.9. The estimated effective transmission rate and the Ro were higher in PL cattle compared to AL cattle. The WBC test is a convenient alternative that can be considered for risk identification and risk management of BLV infection in dairy herds; particularly in livestock regions where laboratory capacity is limited (e.g., use of PCR or gene sequencing techniques) and/or molecular tests are not cost-effective. Therefore, when prevalence of infection is high, the removal of PL cattle should be engaged to control BLV within-herds. [ABSTRACT FROM AUTHOR]

Several viruses have been implicated in breast cancer, including human herpes virus 4 (HHV4), human herpes virus 5 (HHV5), human papilloma virus (HPV), human JC polyoma virus (JCV), human endogenous retrovirus group K (HERVK), bovine leukemia virus (BLV) and mouse mammary tumor virus (MMTV). Human leukocyte antigen (HLA) is involved in virus elimination and has been shown to influence breast cancer protection/susceptibility. Here we investigated the hypothesis that the contribution of a virus to development of breast cancer would depend on the presence of the virus, which, in turn, would be inversely related to the success of its elimination. For that purpose, we estimated in silico predicted binding affinities (PBA) of proteins of the 7 viruses above to 127 common HLA alleles (69 Class I [HLA-I] and 58 Class II HLA-II]) and investigated the association of these binding affinities to the breast cancer—HLA (BC-HLA) immunogenetic profile of the same alleles. Using hierarchical tree clustering, we found that, for HLA-I, viruses BLV, JCV and MMTV were grouped with the BC-HLA, whereas, for HLA-II, viruses BLV, HERVK, HPV, JCV, and MMTV were grouped with BC-HLA. Finally, for both HLA classes, the average PBAs of the viruses grouped with the BC-HLA profile were significantly lower than those of the other, non BC-HLA associated viruses. Assuming that low PBAs are likely associated with slower viral elimination, these findings support the hypothesis that a defective/slower elimination and, hence, longer persistence and inefficient/delayed production of antibodies against them underlies the observed association of the low-PBA group with breast cancer. [ABSTRACT FROM AUTHOR]

Bovine leukemia virus (BLV) is prevalent worldwide, causing serious problems in the cattle industry. The BLV proviral load (PVL) is a useful index for estimating disease progression and transmission risk. We previously developed a quantitative real-time PCR (qPCR) assay to measure the PVL using the coordination of common motif (CoCoMo) degenerate primers. Here, we constructed a novel duplex BLV-CoCoMo qPCR assay that can amplify two genes simultaneously using a FAM-labeled MGB probe for the BLV LTR gene and a VIC-labeled MGB probe for the BoLA-DRA gene. This liquid duplex assay maintained its original sensitivity and reproducibility in field samples. Furthermore, we developed a dry duplex assay composed of PCR reagents necessary for the optimized liquid duplex assay. We observed a strong positive correlation between the PVLs measured using the dry and liquid duplex assays. Validation analyses showed that the sensitivity of the dry duplex assay was slightly lower than that of the other methods for the detection of a BLV molecular clone, but it showed similar sensitivity to the singleplex assay and slightly higher sensitivity than the liquid duplex assay for the PVL quantification of 82 field samples. Thus, our liquid and dry duplex assays are useful for measuring the BLV PVL in field samples, similar to the original singleplex assay. [ABSTRACT FROM AUTHOR]

We investigated the prevalence and spatial distribution of selected pathogens associated with infectious diseases of dairy cattle in Ontario, Canada. The cross-sectional study surveyed bulk tank milk for antibodies against bovine leukemia virus (BLV), Mycobacterium avium ssp. paratuberculosis (MAP), and Salmonella Dublin, and for the presence of mastitis pathogens (Staphylococcus aureus , Streptococcus agalactiae , Mycoplasma bovis). Between October 2021 and June 2022, bulk tank milk samples were obtained from every commercial dairy farm in Ontario (n = 3,286). Samples underwent ELISA testing for the presence of BLV, MAP, and S. Dublin antibodies, and quantitative PCR testing for the detection of specific antigens of pathogens associated with mastitis. Bayesian models were used to estimate prevalence, and spatial analysis was carried out to identify regional clusters of high pathogen prevalence. Prevalence varied for different pathogens, and BLV was widespread across dairy farms in Ontario, with an estimated prevalence of 88.3%. The prevalence of MAP, Staph. aureus and S. Dublin in Ontario dairy herds was 39.8%, 31.5%, and 5.1%, respectively. The vast majority of dairy herds in Ontario were free of intramammary infections caused by Strep. agalactiae and M. bovis. Clusters of increased positive test rates were detected for S. Dublin, MAP, and Staph. aureus , indicating potential geographic risk factors for pathogen transmission. For S. Dublin, an area of increased test positivity rates was detected in southwestern Ontario, close to the Canada-United States border where most of the dairy herds in Ontario are located. Conversely, a localized cluster of positive test outcomes involving 14 subdivisions located in the southeastern region of Ontario was detected for Staph. aureus. Findings from our survey highlight the importance of the testing of aggregated samples and conducting spatial analysis as part of disease surveillance programs, and for implementing risk-based trading approaches among dairy producers. [ABSTRACT FROM AUTHOR]

The investigation into the potential association between retroviruses and breast cancer (BC) presents a fascinating area of research. In this study, the focus was on assessing the presence of two retroviruses, Mouse Mammary Tumor Virus (MMTV) and Bovine Leukemia Virus (BLV), in BC samples and exploring their relationship with relevant clinicopathological variables. The study involved analyzing BC samples from 103 Jordanian female patients diagnosed with BC, as well as breast tissue samples from 25 control patients without evidence of breast malignancy. Real-time PCR was used to investigate the evidence of MMTV and BLV infection in these samples, and the findings were then correlated with various clinicopathological characteristics of BC. The results showed that BLV was detected in 19 (18.4%) of the BC samples, while MMTV was detected in only seven (6.8%). Importantly, none of the control samples tested positive for MMTV or BLV. Additionally, MMTV/BLV co-infections were reported in 1.9% of the BC cases. However, the analysis did not reveal any statistically significant associations between the presence of these retroviruses and various clinicopathological variables, such as age, molecular subtypes of BC, stage, grade, lymph node involvement, tumor size, smoking status, or family history. Despite these findings, it is crucial to acknowledge that further investigation with a larger cohort is necessary to establish a clearer association and elucidate the underlying mechanisms that may explain the exact role of retroviruses in breast carcinogenesis. This study provides insights into the potential infection by MMTV and BLV of BC and lays the groundwork for future research in this area. [ABSTRACT FROM AUTHOR]

Breast cancer is the most common malignancy in the female sex; although recent therapies have significantly changed the natural history of this cancer, it remains a significant challenge. In the past decade, evidence has been put forward that some oncogenic viruses may play a role in the development of sporadic breast cancer; however, data are scattered and mostly reported as sparse case series or small case–control studies. In this review, we organize and report current evidence regarding the role of high-risk human papillomavirus, mouse mammary tumor virus, Epstein–Barr virus, cytomegalovirus, bovine leukemia virus, human polyomavirus 2, and Merkel cell polyomavirus in the pathogenesis of breast cancer. [ABSTRACT FROM AUTHOR]

To identify a biomarker for the early diagnosis of enzootic bovine leukosis (EBL) caused by bovine leukemia virus (BLV), we investigated the expression of a microRNA, bta-miR-375, in cattle serum. Using quantitative reverse-transcriptase PCR analysis, we measured bta-miR-375 levels in 27 samples from cattle with EBL (EBL cattle), 45 samples from animals infected with BLV but showing no clinical signs (NS cattle), and 30 samples from cattle uninfected with BLV (BLV negative cattle). In this study, we also compared the kinetics of bta-miR-375 with those of the conventional biomarkers of proviral load (PVL), lactate dehydrogenase (LDH), and thymidine kinase (TK) from the no-clinical-sign phase until EBL onset in three BLV-infected Japanese black (JB) cattle. Bta-miR-375 expression was higher in NS cattle than in BLV negative cattle (P < 0.05) and greater in EBL cattle than in BLV negative and NS cattle (P < 0.0001 for both comparisons). Receiver operating characteristic curves demonstrated that bta-miR-375 levels distinguished EBL cattle from NS cattle with high sensitivity and specificity. In NS cattle, bta-miR-375 expression was increased as early as at 2 months before EBL onset—earlier than the expression of PVL, TK, or LDH isoenzymes 2 and 3. These results suggest that serum miR-375 is a promising biomarker for the early diagnosis of EBL. [ABSTRACT FROM AUTHOR]

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OBJECTIVE: The objective of this study was to determine the seroprevalence of reproductive and infectious diseases in tropical cattle in the Tambopata and Tahuamanu Provinces in the department of Madre de Dios, Peru. SAMPLE: 156 bovines from 7 cattle farms were sampled. These farms used exclusive grazing for food and natural mating for reproduction and did not have sanitary or vaccination programs. METHODS: The serum of blood samples was subjected to ELISA with commercial kits for the detection of antibodies against Neospora caninum, Mycobacterium avium subsp paratuberculosis (MAP), Leptospira interrogans, pestivirus bovine viral diarrhea virus-1, retrovirus bovine leukemia virus (BLV), orbivirus bluetongue virus (BTV), and herpesvirus bovine herpes virus-1 (BHV). The data were analyzed by means of association tests with χ2 (P < .05) and Spearman rank correlation (P < .05) in the SPSS v.15.0 software (IBM Corp). RESULTS: A low prevalence of antibodies to L interrogans, N caninum, M avium subsp paratuberculosis, bovine viral diarrhea virus-1 was found, but it was high to BTV, BLV, and BHV (100%, 53.85%, and 72.44%, respectively). The presence of BLV and BHV was higher in the Las Piedras District, bovines less than 5 years old, and cattle with breed characteristics of zebu and crossbred (P < .01). In addition, there was a significant correlation between both infections, showing 83.3% of BLV positivity that were also BHV positive (P < .01). CLINICAL RELEVANCE: The high prevalence of antibodies to BTV, BHV, and BLV could be due to livestock management practices, direct contact with infected animals, and variation of the presence of vectors and natural reservoirs in the context of climate change in the tropics. [ABSTRACT FROM AUTHOR]

OBJECTIVE To establish a threshold value of bovine leukemia virus (BLV) proviral load (PVL) to identify increased risk of severe clinical mastitis, and to examine the prognosis and economic loss of clinical mastitis based on the newly established PVL cut-off value. ANIMALS 97 lactating Holstein cows with clinical mastitis. METHODS Blood and milk samples were collected aseptically from each cow. Youden index was used for receiver-operating characteristic curve analysis with the severity rate of clinical mastitis as the dependent variable and PVL as an independent variable. PVL cut-off value was used as a criterion to compare the severity rate of clinical mastitis, percentage of cows with and without systemic treatments, number of treatments, cost of treatment, and prognosis. RESULTS PVL cut-off value was 17.8 copies/10 ng DNA for the dependent variable MILD vs SEVERE. The severity rate of clinical mastitis, percentage of cows given systemic treatments, and technical fees for medical treatment were significantly higher in the group above the PVL cut-off value than in the group below the PVL cut-off value and the negative group. Number of treatments was significantly higher in the group above the cut-off value than in the group below the cut-off value. There was no significant difference in prognosis after mastitis among the 3 groups. CLINICAL RELEVANCE These results suggested that PVL cut-off value of 17.8 copies/10 ng DNA was a useful threshold for increased economic losses in BLV-infected cows; it may also serve as a new standard value for the detection and culling of BLV-infected cows in Japan. [ABSTRACT FROM AUTHOR]

Bovine leukemia virus (BLV) establishes a lifelong persistent infection in dairy cattle. White blood cell count (WBC) is correlated with proviral load in the blood and milk of BLV-infected cattle, and testing WBC can be used to assess both BLV infectiousness levels and risk of BLV transmission from different types of infected animals. The objective of the study was to compare effective transmission rates (β) and the basic reproduction ratio (Ro) among two types of BLV-infected dairy cows in Chile: those affected with persistent lymphocytosis (PL) vs. aleukemic (AL).The estimated (β) coefficient was higher in PL cattle [1.1; 95% Confidence interval (CI) (−1.6, 3.8)], compared to AL cattle (−3.1; 95% CI = −3.7, −2.5). In addition, the Ro was higher in PL cattle (60.4; 95% CI = 3.5; 820.6), compared to AL cattle (1.5; 95% CI = 0.7, 3.1). The ratio between PL/AL expected rate of cases was 73.9. The estimated effective transmission rate and the Ro were higher in PL cattle compared to AL cattle. The WBC test is a convenient alternative that can be considered for risk identification and risk management of BLV infection in dairy herds; particularly in livestock regions where laboratory capacity is limited (e.g., use of PCR or gene sequencing techniques) and/or molecular tests are not cost-effective. Therefore, when prevalence of infection is high, the removal of PL cattle should be engaged to control BLV within-herds.

This document is a summary of a special issue of the journal Viruses titled "Novel Diagnostic Technologies for SARS-CoV-2 and Other Emerging Viruses." The special issue focuses on the development of new and effective technologies for detecting viruses, including SARS-CoV-2, using various diagnostic methods such as nucleic acid amplification, antigen detection, and next-generation sequencing. The articles in the special issue cover topics such as virus detection in food and environmental samples, analysis of SARS-CoV-2 sequencing data, detection of SARS-CoV-2 RNA and proteins in exosomes, quantum dot technology for clinical diagnosis, and a fusion assay for studying SARS-CoV-2 entry. The authors emphasize the need for continuous development of cost-effective and high-throughput diagnostic technologies to detect viruses and their genetic mutations, as well as the importance of surveillance for zoonotic viruses. [Extracted from the article]

The article titled "Image challenge in Veterinary Pathology" presents a series of images depicting various pathological conditions in animals. The images include examples such as endometriosis, epidermoid cysts, ovarian follicular cysts, and dermoid cysts. Each image is accompanied by a multiple-choice question asking readers to identify the diagnosis or predisposing factors. The answers to these questions can be found in the Veterinary Pathology journal. [Extracted from the article]

The present study analyzed B-cell clonality and bovine leukemia virus (BLV) provirus integration sites in cattle with enzootic bovine leukosis (EBL) having BLV proviral copy numbers less or greater than the number of bovine nucleated cells. EBL cattle with BLV copy numbers less than the number of bovine nucleated cells showed monoclonal and biclonal proliferation of B-cells with one BLV provirus integration site. On the other hand, EBL cattle with BLV copy numbers greater than the number of bovine nucleated cells showed monoclonal proliferation of B-cells with two BLV provirus integration sites. These results suggest that superinfection of BLV can occur in EBL cattle. [ABSTRACT FROM AUTHOR]

ABSTRACT: Bovine leukemia virus (BLV) has spread worldwide and causes serious problems in the cattle industry owing to the lack of effective treatments and vaccines. Bovine leukemia virus is transmitted via horizontal and vertical infection, and cattle with high BLV proviral load (PVL), which is a useful index for estimating disease progression and transmission risk, are considered major infectious sources within herds. The PVL strongly correlates with highly polymorphic bovine lymphocyte antigen (BoLA)-DRB3 alleles. The BoLA-DRB3*015:01 and *012:01 alleles are known susceptibility-associated markers related to high PVL, and cattle with susceptible alleles may be at a high risk of BLV transmission via direct contact with healthy cows. In contrast, the BoLA-DRB3*009:02 and *014:01:01 alleles comprise resistant markers associated with the development of low PVL, and cattle with resistant alleles may be low-risk spreaders for BLV transmission and disrupt the BLV transmission chain. However, whether polymorphisms in BoLA-DRB3 are useful for BLV eradication in farms remains unknown. Here, we conducted a validation trial of the integrated BLV eradication strategy to prevent new infection by resistant cattle and actively eliminate susceptible cattle in addition to conventional BLV eradication strategies to maximally reduce the BLV prevalence and PVL using a total of 342 cattle at 4 stall-barn farms in Japan from 2017 to 2019. First, we placed the resistant milking cattle between the BLV-positive and BLV-negative milking cattle in a stall barn for 3 yr. Interestingly, the resistant cattle proved to be an effective biological barrier to successfully block the new BLV infections in the stall-barn system among all 4 farms. Concomitantly, we actively eliminated cattle with high PVL, especially susceptible cattle. Indeed, 39 of the 60 susceptible cattle (65%), 76 of the 140 neutral cattle (54%), and 20 of the 41 resistant cattle (48.8%) were culled on 4 farms for 3 years. Consequently, BLV prevalence and mean PVL decreased in all 4 farms. In particular, one farm achieved BLV-free status in May 2020. By decreasing the number of BLV-positive animals, the revenue-enhancing effect was estimated to be ¥5,839,262 ($39,292.39) for the 4 farms over 3 yr. Our results suggest that an integrated BLV eradication program utilization of resistant cattle as a biological barrier and the preferential elimination of susceptible cattle are useful for BLV infection control.

Enzootic bovine leukosis (EBL) is B-cell lymphoma in cattle caused by bovine leukemia virus (BLV) infection. The incidence of EBL has been increasing since 1998 in Japan, resulting in significant economic losses for farms. The BLV genome integrates with the host genome as provirus, leading to sustainably infection. Although most of the BLV-infected cattle are aleukemic, some cattle cause persistent lymphocytosis (PL) and subsequently develop EBL. Recent reports suggest the association between the risk for the transmission of BLV and the developing EBL and the proviral load (PVL) in BLV-infected cattle, which cannot measure readily in the field. This study aims to build a statistical model for predicting PVL of BLV-infected asymptomatic or PL cattle based on data accessible in the field. Five negative binomial regression models with different linear predictors were built and compared for the predictability of PVL. Consequently, the model with two explanatory variables (age in months and logarithm of lymphocyte count) was selected as the best model. The model can be used in the field as a cost-beneficial supporting tool to estimate the risk of transmission of BLV and developing EBL in infected cattle. [ABSTRACT FROM AUTHOR]

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leucosis (EBL), which affects cattle globally. In Egypt, BLV control strategies have been ignored because of the shortage of BLV research studies and the silent infection in most animals. This study aimed to identify the risk factors associated with the prevalence of BLV among dairy and beef cattle from six different geographic and climatic provinces in Egypt. Additionally, risk factors affecting the BLV proviral load (PVL) among the positive cattle were targeted. The total BLV prevalence in cattle from six investigated Egyptian provinces was 24.2% (105/433), while the mean PVL (8651.6 copies /105 white blood cells) was absolutely high as estimated by the BLV-CoCoMo-quantitative polymerase chain reaction (qPCR)-2 assay. Analysis of the influence of risk factors (age, sex, breed, production type, farm size, and location) on BLV prevalence indicated that the Holstein breed (OR = 1.582, p = 0.007), beef cattle (OR = 1.088, p = 0.0001), large-size farms (OR = 1.26, p = 0.0001), and cattle from Damietta (OR = 1.43, p = 0.0001) and Cairo (OR = 1.16, p = 0.0001) were ultimately proven the most important risks for BLV infection. The risk factors were analyzed considering the BLV PVL levels in the BLV-positive cases. Significantly high PVL (HPVL) levels were observed in cattle > 5 years old (p < 0.0001), females (p = 0.0008), Holstein (p < 0.0001), dairy cows (p = 0.0053), large-size farms (p < 0.0001), and cattle from Damietta (p < 0.0001) compared to other categories. Contrary, no significant differences in PVL levels were reported between the Native and Mixed cattle breeds (p = 0.13). Ultimately, the logistic regression model indicated that the probability of carrying HPVL in cattle > 5 years is 1.27 (95% CI: 1.03–2.09, p < 0.001) times more likely compared to cattle < 2 years old. In conclusion, the findings were valuably correlating the BLV prevalence with PVL as an indicator of the risk of BLV infection. [ABSTRACT FROM AUTHOR]

We have characterized the intrahost genetic variation in the bovine leukemia virus (BLV) by examining 16 BLV isolates originating from the Western Siberia–Tyumen and South Ural–Chelyabinsk regions of Russia. Our research focused on determining the genetic composition of an 804 bp fragment of the BLV env gene, encoding for the entire gp51 protein. The results provide the first indication of the quasi-species genetic nature of BLV infection and its relevance for genome-level variation. Furthermore, this is the first phylogenetic evidence for the existence of a dual infection with BLV strains belonging to different genotypes within the same host: G4 and G7. We identified eight cases of recombination between these two BLV genotypes. The detection of quasi-species with cases of dual infection and recombination indicated a higher potential of BLV for genetic variability at the intra-host level than was previously considered. [ABSTRACT FROM AUTHOR]

Simple Summary: Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis (EBL), which is the most significant neoplastic disease in cattle. EBL is often overlooked in daily breeding processes due to the absence of obvious clinical symptoms. However, studies have revealed that EBL can severely impact the production performance of dairy cows, leading to a substantial economic burden on the cattle industry. In recent years, the global prevalence of EBL has been on the rise, and fragments of BLV nucleic acid have been detected in human breast cancer patients, raising public concerns. Due to the absence of an effective vaccine, controlling the disease is challenging. This review aims to provide a comprehensive overview of BLV, including its role in causing EBL, the genome of BLV, its current prevalence, transmission routes, clinical symptoms, detection methods, hazards, control strategies, and the current state of BLV research. The primary objective of this review is to offer breeders and researchers reliable veterinary knowledge on BLV and identify future research directions in this field. Bovine leukemia virus (BLV) is a retrovirus that causes enzootic bovine leucosis (EBL), which is the most significant neoplastic disease in cattle. Although EBL has been successfully eradicated in most European countries, infections continue to rise in Argentina, Brazil, Canada, Japan, and the United States. BLV imposes a substantial economic burden on the cattle industry, particularly in dairy farming, as it leads to a decline in animal production performance and increases the risk of disease. Moreover, trade restrictions on diseased animals and products between countries and regions further exacerbate the problem. Recent studies have also identified fragments of BLV nucleic acid in human breast cancer tissues, raising concerns for public health. Due to the absence of an effective vaccine, controlling the disease is challenging. Therefore, it is crucial to accurately detect and diagnose BLV at an early stage to control its spread and minimize economic losses. This review provides a comprehensive examination of BLV, encompassing its genomic structure, epidemiology, modes of transmission, clinical symptoms, detection methods, hazards, and control strategies. The aim is to provide strategic information for future BLV research. [ABSTRACT FROM AUTHOR]

Bovine leukemia virus (BLV) is a retrovirus whose target cell is B lymphocytes, which has a negative impact on the immune system of infected animals, making them more susceptible to other diseases of infectious origin. The objective of this work was to carry out a sanitary study of infectious diseases in a specialized dairy herd in the department of Antioquia and to analyze their possible association with BLV infection. 87 blood samples were taken from Holstein Friesian cows to which an indirect ELISA was performed for the gp51 protein of the virus. The presence/absence data for three diseases (anaplasmosis, mastitis and metritis) and the fever sign were recorded for each of the bovines analyzed during the period of time from 2006 to 2014. The data was analyzed through 2x2 contingency tables and Odds Ratio (OR). The serological prevalence of BLV in the herd was 82.75% and the presentation of diseases during the years 2006 and 2014 was 38.27% for mastitis, 19.58% for anaplasmosis, 15.13% for metritis and 27% for fever. According to the magnitude of effect for the OR, it was found that in general the BLV seroprevalence has an insignificant association with the diseases; however, a moderate association with the fever sign was recorded. Fever is a sign that is associated with infections and it is possible that the decreased immune response to BLV is correlated with the presentation of other infectious diseases. [ABSTRACT FROM AUTHOR]

Bovine leukosis is a disease caused by an oncogenic retrovirus that belongs to the Retroviridae family and is known for its worldwide distribution, causing great economic losses, especially in dairy farming. Few studies on the disease have been reported in Risaralda (Colombia). The objective was to determine the prevalence of the bovine leukosis virus and its association with some risk/protection factors in cattle herds from Risaralda. Blood samples were taken from 145 individuals from 6 herds in the Risaralda region, during the year 2018. DNA extraction was carried out by salting out and PCR was used to detect the provirus DNA. For each animal, the racial composition, sex, age group, origin and herd were taken in order to evaluate possible factors associated with the presence of the virus. A descriptive analysis of the information was performed, the prevalence was estimated with the 95% confidence interval, and the effect of risk/protection factors on leukosis positivity was determined by logistic regression and the odds ratio was estimated. All analyzes were done using R software. A general prevalence of 6.90% was estimated. Statistically significant differences were found for age group one (Under 5 years) and two (5 to 10 years) with respect to age group three (Over 10 years) (OR = 0.19 in both cases), indicating a higher frequency with age. This work is one of the first carried out in the department of Risaralda and provides surveillance of the disease in Colombia. [ABSTRACT FROM AUTHOR]

The objective was to evaluate the effects of bovine leukemia virus (BLV) infection, as determined by BLV seropositivity and proviral load, on 305-d milk, fat, and protein production of dairy cows. A cross-sectional study was conducted among 1,712 cows from 9 dairy herds in Alberta, Canada. The BLV status was assessed using an antibody ELISA, whereas BLV proviral load in BLV-seropositive cattle was determined with quantitative PCR. Dairy Herd Improvement 305-d milk, fat, and protein production data were obtained for all enrolled cattle. Differences in these milk end points were assessed in 2 ways: first, by categorizing cows based on BLV serostatus (i.e., BLV positive or negative), and second, by categorizing based on BLV proviral load (i.e., BLV negative, low proviral load [LPL] BLV positive, and high proviral load [HPL] BLV positive). A mixed-effect multivariable linear regression model was used to assess differences in milk parameters. We found that BLV positivity, adjusted for parity and natural log-transformed somatic cell count (SCC), was not associated with reduction in 305-d milk, fat, or protein production. However, significant reductions in 305-d milk, fat, and protein yield occurred in HPL cows, but not in LPL cows, compared with BLV-negative cows, when adjusted for parity number and natural log-transformed SCC. In summary, BLV proviral load may predict effects of BLV infection on milk, fat, and protein production. [ABSTRACT FROM AUTHOR]

Simple Summary: Bovine leukemia virus (BLV) is a retrovirus found in cattle, which reduces the lifespan of infected cows and is significantly associated with the occurrence of mastitis in dairy herds. A thorough understanding of the impacts and mechanisms of BLV on the antimicrobial defense function of mammary epithelial cells in dairy cows is essential for preventing and managing bovine mastitis. BLV-encoded microRNAs (BLV-miRNAs) represent functional components that contribute to oncogenesis. This study aimed to examine how BLV-miR-B1-5p promotes Staphylococcus aureus (S. aureus) adhesion to bovine mammary epithelial (MAC-T) cells via miRNA target gene prediction and validation. The results indicate that BLV-miR-B1-5p promotes S. aureus adhesion to bovine mammary epithelial cells by targeting mucin 1 (MUC1). Bovine leukemia virus (BLV) is widely prevalent worldwide and can persistently infect mammary epithelial cells in dairy cows, leading to reduced cellular antimicrobial capacity. BLV-encoded microRNAs (BLV-miRNAs) can modify host genes and promote BLV replication. We previously showed that BLV-miR-B1-5p significantly promoted Staphylococcus aureus (S. aureus) adhesion to bovine mammary epithelial (MAC-T) cells; however, the pathway responsible for this effect remained unclear. This study aims to examine how BLV-miR-B1-5p promotes S. aureus adhesion to MAC-T cells via miRNA target gene prediction and validation. Target site prediction showed that BLV-miR-B1-5p could target the mucin family gene mucin 1 (MUC1). Real-time polymerase chain reaction, immunofluorescence, and dual luciferase reporter assay further confirmed that BLV-miR-B1-5p could target and inhibit the expression of MUC1 in bovine MAC-T cells while interfering with the expression of MUC1 promoted S. aureus adhesion to MAC-T cells. These results indicate that BLV-miR-B1-5p promotes S. aureus adhesion to mammary epithelial cells by targeting MUC1. [ABSTRACT FROM AUTHOR]

Background: Enzootic bovine leukosis (EBL) is a lymphoproliferative disorder caused by the bovine leukemia virus (BLV), a virus of the Retroviridae family. The infection is distributed worldwide, and a high percentage of animals infected by the BLV are asymptomatic and act as carriers of the virus in many cattle populations. Aim: To identify the risk factors associated with EBL in the municipalities of Boyacá and Cundinamarca (Colombia). Methods: A simple descriptive cross-sectional study with random sampling was conducted. A total of 1,140 blood samples were taken from cattle (females and males) from the municipalities of Chiquinquirá, Ubaté, and San Miguel de Sema of different breeds and age groups. The samples were processed using the commercial ELISA SERELISA® BLV Ab Mono Blocking kit (sensitivity 97%, specificity 98%). The data were processed with the statistical programs WinEpi and Epi Info® version 7.2.4.0, estimating the prevalence ratio, implementing the chi-square test (p ≤ 0.05) and logistic regression. Results: A true prevalence (TP) and apparent prevalence (AP) of 23.61% and 22.7% in Ubaté, 19.22% and 18.1% in Chiquinquirá, and 15.61% and 14.3% in San Miguel de Sema, respectively, were established. Bovines 2-4 years old were the most prevalent in Ubaté and Chiquinquirá (37.5% and 21.21%, respectively), while in San Miguel de Sema individuals >4 years had the highest percentage of antibodies (18.3%). The Holstein breed had a higher prevalence in Ubaté and San Miguel de Sema (26.02% and 19.67%), and crossbreeds were more BLV-seroprevalence in Chiquinquirá (20.20%). In Ubaté, re-use of needles was identified as a risk factor, contaminated blood in needles is considered one of the main routes of transmission. On the other hand, manual milking was identified as a risk factor in San Miguel de Sema. Conclusion: The non-implementation of an individual needle per animal in Ubaté; the Holstein breed and manual milking in San Miguel de Sema were identified as risk factors for the presence of antibodies against the disease. EBL prevention and control plans should be established that focus on the implementation of management and sanitary practices based on herd biosecurity. [ABSTRACT FROM AUTHOR]

Bovine leukemia virus (BLV) has spread worldwide and causes serious problems in the cattle industry owing to the lack of effective treatments and vaccines. Bovine leukemia virus is transmitted via horizontal and vertical infection, and cattle with high BLV proviral load (PVL), which is a useful index for estimating disease progression and transmission risk, are considered major infectious sources within herds. The PVL strongly correlates with highly polymorphic bovine lymphocyte antigen (BoLA)- DRB3 alleles. The BoLA-DRB3*015:01 and *012:01 alleles are known susceptibility-associated markers related to high PVL, and cattle with susceptible alleles may be at a high risk of BLV transmission via direct contact with healthy cows. In contrast, the BoLA-DRB3*009:02 and *014:01:01 alleles comprise resistant markers associated with the development of low PVL, and cattle with resistant alleles may be low-risk spreaders for BLV transmission and disrupt the BLV transmission chain. However, whether polymorphisms in BoLA-DRB3 are useful for BLV eradication in farms remains unknown. Here, we conducted a validation trial of the integrated BLV eradication strategy to prevent new infection by resistant cattle and actively eliminate susceptible cattle in addition to conventional BLV eradication strategies to maximally reduce the BLV prevalence and PVL using a total of 342 cattle at 4 stall-barn farms in Japan from 2017 to 2019. First, we placed the resistant milking cattle between the BLV-positive and BLV-negative milking cattle in a stall barn for 3 yr. Interestingly, the resistant cattle proved to be an effective biological barrier to successfully block the new BLV infections in the stall-barn system among all 4 farms. Concomitantly, we actively eliminated cattle with high PVL, especially susceptible cattle. Indeed, 39 of the 60 susceptible cattle (65%), 76 of the 140 neutral cattle (54%), and 20 of the 41 resistant cattle (48.8%) were culled on 4 farms for 3 years. Consequently, BLV prevalence and mean PVL decreased in all 4 farms. In particular, one farm achieved BLV-free status in May 2020. By decreasing the number of BLV-positive animals, the revenue-enhancing effect was estimated to be ¥5,839,262 ($39,292.39) for the 4 farms over 3 yr. Our results suggest that an integrated BLV eradication program utilization of resistant cattle as a biological barrier and the preferential elimination of susceptible cattle are useful for BLV infection control. [ABSTRACT FROM AUTHOR]

A 23-month-old Holstein-Friesian heifer presented with inactivity and diarrhea. On physical examination, no enlargement of superficial lymph nodes was observed. Hematological examination revealed lymphocytosis. The bovine leukemia virus (BLV) proviral load was 2,122 copies/10 ng DNA, and BLV was classified as Group C based on whole genome phylogenetic analysis. Monoclonal proliferation of B-cells and monoclonal integration of the BLV provirus in the bovine genome were detected by a clonality test of B-cells and inverse PCR, respectively. Although lymph nodes were not swollen at necropsy, histopathological examination revealed neoplastic lymphocyte proliferation in lymph nodes, which were immune positive for CD5 and CD20, and negative for CD3. The heifer was diagnosed with EBL caused by BLV classified as Group C. [ABSTRACT FROM AUTHOR]

B‐cell leukemia is a rare form of hematologic neoplasia in sheep, especially in adult animals. We present a case report of a 5‐year‐old WhiteFace Sheep wether with suspected acute lymphoblastic leukemia. The patient, a second‐generation relative of ewes experimentally inoculated with atypical scrapie, exhibited acute lethargy and loss of appetite. Laboratory investigation revealed marked leukocytosis, lymphocytosis, and abnormal serum chemistry panel results. Microscopic examination of blood and bone marrow smears exhibited a high percentage of large neoplastic cells with lymphoid characteristics. Histopathologic analysis of the spleen, liver, lungs, and other organs confirmed the presence of widespread tissue infiltration by neoplastic cells. Immunohistochemical labeling demonstrated strong intracytoplasmic labeling for CD20, consistent with B‐cell neoplasia. Flow cytometric analysis confirmed the B‐cell lineage of the neoplastic cells. Screening for bovine leukemia virus, which can experimentally cause leukemia in sheep, yielded a negative result. In this case, the diagnosis of B‐cell leukemia was supported by a comprehensive panel of diagnostic evaluations, including cytology, histopathology, immunohistochemistry, and immunophenotyping. This case report highlights the significance of accurate diagnosis and classification of hematologic neoplasia in sheep, emphasizing the need for immunophenotyping to aid in the diagnosis of B‐cell leukemia. It also emphasizes the importance of considering spontaneous leukemia as a differential diagnosis in sheep with lymphoid neoplasia, especially in the absence of circulating infectious diseases. [ABSTRACT FROM AUTHOR]

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis, the most prevalent neoplastic disease of cattle worldwide. The immune response to BLV and disease susceptibility and resistance in cattle are strongly correlated with the bovine leukocyte antigen (BoLA)-DRB3 allelic polymorphism. BLV infection continues to spread in Egypt, in part because the relationships between BLV infection, proviral load in Egypt, and BoLA-DRB3 polymorphism are unknown. Here, we identified 18 previously reported alleles in 121 Holstein cows using a polymerase chain reaction sequence-based typing method. Furthermore, BoLA-DRB3 gene polymorphisms in these animals were investigated for their influence on viral infection. BoLA-DRB3*015:01 and BoLA-DRB3*010:01 were identified as susceptible and resistant alleles, respectively, for BLV infection in the tested Holsteins. In addition, BoLA-DRB3*012:01 was associated with low PVL in previous reports but high PVL in Holstein cattle in Egypt. This study is the first to demonstrate that the BoLA-DRB3 polymorphism confers resistance and susceptibility to PVL and infections of BLV in Holstein cattle in Egypt. Our results can be useful for the disease control and eradication of BLV through genetic selection. [ABSTRACT FROM AUTHOR]

Enzootic bovine leukemia is an infectious disease with a chronic course caused by an RNA‑containing virus of the genus Deltaretrovirus. Despite the implementation of various programs for the elimination of leukemia, the disease is still widespread on the planet and continues to cause significant economic damage. A large proportion of BLV‑infected cattle remain to be asymptomatic carriers of the virus, which complicates diagnosis and contributes to the spread of the disease in the herd. The structure of the BLV genome is generally typical of retroviruses. It consists of genes encoding structural proteins, viral enzymes and regulatory elements flanked on both sides by identical long terminal repeats. The enzyme and structural protein coding genes (gag, pro, pol, and env) play a crucial role in the life cycle of the virus, influencing its infectivity and virion production. The tax and rex regulatory genes regulate viral transcription, export of transcripts from the nucleus to the cytoplasm, and disease progression. The increase in the number of copies of proviral DNA occurs mainly not due to the functioning of the virus reverse transcriptase, but because of clonal reproduction of the affected subpopulations of B‑cells, mainly CD5+ IgM+. This feature provides increased genetic stability of the BLV virus. These properties of the viral genome allow the development of a variety of PCR test systems. The widespread implementation of such systems enables the detection of carriers of the disease at early stages, which should contribute to the effective implementation of national programs to eradicate bovine leukemia.

Bovine leukemia virus (BLV) is known as the causative agent of enzootic bovine leukosis (EBL), which is a worldwide distributed disease and has also been detected in marketed beef and dairy products. BLV causes significant economic losses due to the loss of milk and yield or the slaughter of animals without adequate development. It has been reported in epidemiological studies that this infection is common in Türkiye, especially in the western provinces. There is no data on the possible presence or prevalence of BLV infection and its seroepidemiology in Muş province. The aim of this study is to determine the possible presence and prevalence of the infection, its role in yield losses, and to obtain epidemiological data on cattle farming in the Muş district. For this purpose, 300 blood serum samples were collected from cattle aged six months and older in the province of Muş and its different districts. The blood serum samples taken were tested for the presence of BLV-specific antibodies by agar gel immunodiffusion (AGID) and competitive enzyme-linked immunosorbent assay (C-ELISA) methods. As a result of the study, all of the controlled districts were evaluated as negative in the AGID and C-ELISA tests for the presence of BLV-specific antibodies. In conclusion, for the first time, it was demonstrated that cattle farming in the Muş province were BLV-free during the sampling period. Although BLV seropositivity was not detected in the tested animals, it is emphasized that the control of infection and eradication program should not be ignored.

Abstract Background The Kumamoto strain of Japanese Brown (JBRK) cattle is a sub-breed of Wagyu and has a different genetic background than that of Japanese Black (JB) cattle. Bovine leukemia virus (BLV) is the pathogen causing enzootic bovine leukosis (EBL), the predominant type of bovine leukosis (BL). EBL is one of the most common bovine infectious diseases in dairy countries, including Japan. Some host genetic factors, including the bovine leukocyte antigen (BoLA)-DRB3 gene, have been associated with the proviral load (PVL) of BLV and/or onset of EBL. Here, we determined the number of BL cases by analyzing prefectural case records in detail. We measured the PVL of BLV-infected JBRK cattle and compared it with that obtained for other major breeds, JB and Holstein-Friesian (HF) cattle. Finally, the relationship between PVL levels and BoLA-DRB3 haplotypes was investigated in BLV-infected JBRK cattle. Results We determined the number of BL cases recorded over the past ten years in Kumamoto Prefecture by cattle breed. A limited number of BL cases was observed in JBRK cattle. The proportion of BL cases in the JBRK was lower than that in JB and HF. The PVL was significantly lower in BLV-infected JBRK cattle than that in the JB and HF breeds. Finally, in BLV-infected JBRK cattle, the PVL was not significantly affected by BoLA-DRB3 alleles and haplotypes. BoLA-DRB3 allelic frequency did not differ between BLV-infected JBRK cattle with low PVL and high PVL. Conclusions To our knowledge, this is the first report showing that BL occurred less in the JBRK population of Kumamoto Prefecture. After BLV-infection, the PVL was significantly lower in JBRK cattle than that in JB and HF breeds. The genetic factors implicated in maintaining a low PVL have yet to be elucidated, but the BoLA-DRB3 haplotypes are likely not involved.

Abstract Background Subclinical infection with bovine leukemia virus (BLV) in cows can cause economic losses in milk and meat production in many countries, as BLV-related negative effects. The volatile fatty acids (VFAs) and microbiota present in the digestive tracts of cows can contribute to cow health. Here, we exploratorily investigated the VFAs and microbiota in the rumen and gut with respect to subclinical BLV infection using cows housed at a single farm. Results We analyzed a herd of 38 cows kept at one farm, which included 15 uninfected and 23 BLV-infected cows. First, the analysis of the VFAs in the rumen, gut, and blood revealed an absence of statistically significant differences between the uninfected and BLV-infected groups. Thus, BLV infection did not cause major changes in VFA levels in all tested specimens. Next, we analyzed the rumen and gut microbiota. The analysis of the microbial diversity revealed a modest difference between the uninfected and BLV-infected groups in the gut; by contrast, no differences were observed in the rumen. In addition, the investigation of the bacteria that were predominant in the uninfected and BLV-infected groups via a differential abundance analysis showed that no significant bacteria were present in either of the microbiota. Thus, BLV infection possibly affected the gut microbiota to a small extent. Moreover, bacterial associations were compared between the uninfected and BLV-infected groups. The results of this analysis suggested that BLV infection affected the equilibrium of the bacterial associations in both microbiota, which might be related to the BLV-related negative effects. Thus, BLV infection may negatively affect the equilibrium of bacterial associations in both microbiota. Conclusions Subclinical BLV infection is likely to affect the rumen and gut microbiota, which may partly explain the BLV-related negative effects.

Enzootic bovine leukosis, a neoplastic disease caused by the bovine leukemia virus (BLV), was the primary cancer affecting cattle in China before 1985. Although its prevalence decreased significantly between 1986 and 2000, enzootic bovine leukosis has been re-emerging since 2000. This re-emergence has been largely overlooked, possibly due to the latent nature of BLV infection or the perceived lack of sufficient evidence. This study investigated the molecular epidemiology of BLV infections in dairy cattle in Henan province, Central China. Blood samples from 668 dairy cattle across nine farms were tested using nested polymerase chain reaction assays targeting the partial envelope (env) gene (gp51 fragment). Twenty-three samples tested positive (animal-level prevalence of 3.4%; 95% confidence interval: 2.2, 5.1). The full-length env gene sequences from these positive samples were obtained and phylogenetically analyzed, along with previously reported sequences from the GenBank database. The sequences from positive samples were clustered into four genotypes (1, 4, 6, and 7). The geographical annotation of the maximum clade credibility trees suggested that the two genotype 1 strains in Henan might have originated from Japan, while the genotype 7 strain is likely to have originated from Moldova. Subsequent Bayesian stochastic search variable selection analysis further indicated a strong geographical association between the Henan strains and Japan, as well as Moldova. The estimated substitution rate for the env gene ranged from 4.39 × 10−4 to 2.38 × 10−3 substitutions per site per year. Additionally, codons 291, 326, 385, and 480 were identified as positively selected sites, potentially associated with membrane fusion, epitope peptide vaccine design, and transmembrane signal transduction. These findings contribute to the broader understanding of BLV epidemiology in Chinese dairy cattle and highlight the need for measures to mitigate further BLV transmission within and between cattle herds in China.