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IntroductionIn 2021, a type 2 vaccine-derived poliovirus (VDPV2) was isolated from the stool of a patient with acute flaccid paralysis (AFP) admitted to Spain from Senegal. A virological investigation was conducted to characterize and trace the origin of VDPV2.MethodsWe used an unbiased metagenomic approach for the whole-genome sequencing of VDPV2 from the stool (pre-treated with chloroform) and from the poliovirus-positive supernatant. Phylogenetic analyses and molecular epidemiological analyses relying on the Bayesian Markov Chain Monte Carlo methodology were used to determine the geographical origin and estimate the date of the initiating dose of the oral poliovirus vaccine for the imported VDPV2.ResultsWe obtained a high percentage of viral reads per total reads mapped to the poliovirus genome (69.5% for pre-treated stool and 75.8% for isolate) with a great depth of sequencing coverage (5,931 and 11,581, respectively) and complete genome coverage (100%). The two key attenuating mutations in the Sabin 2 strain had reverted (A481G in the 5’UTR and Ile143Thr in VP1). In addition, the genome had a recombinant structure between type-2 poliovirus and an unidentified non-polio enterovirus-C (NPEV-C) strain with a crossover point in the protease-2A genomic region. VP1 phylogenetic analysis revealed that this strain is closely related to VDPV2 strains circulating in Senegal in 2021. According to Bayesian phylogenetics, the most recent common ancestor of the imported VDPV2 could date back 2.6 years (95% HPD: 1.7–3.7) in Senegal. We suggest that all VDPV2s circulating in 2020–21 in Senegal, Guinea, Gambia, and Mauritania have an ancestral origin in Senegal estimated around 2015. All 50 stool samples from healthy case contacts collected in Spain (n = 25) and Senegal (n = 25) and four wastewater samples collected in Spain were poliovirus negative.DiscussionBy using a whole-genome sequencing protocol with unbiased metagenomics from the clinical sample and viral isolate with high sequence coverage, efficiency, and throughput, we confirmed the classification of VDPV as a circulating type. The close genomic linkage with strains from Senegal was consistent with their classification as imported. Given the scarce number of complete genome sequences for NPEV-C in public databases, this protocol could help expand poliovirus and NPEV-C sequencing capacity worldwide.

Abstract Comparing pandemic waves could aid in understanding the evolution of COVID-19. The objective of the present study was to compare the characteristics and outcomes of patients hospitalized for COVID-19 in different pandemic waves in terms of severity and mortality. We performed an observational retrospective cohort study of 5,220 patients hospitalized with SARS-CoV-2 infection from February to September 2020 in Aragon, Spain. We compared ICU admissions and 30-day mortality, clinical characteristics, and risk factors of the first and second waves of COVID-19. The SARS-CoV-2 genome was also analyzed in 236 samples. Patients in the first wave (n = 2,547) were older (median age 74 years [IQR 60–86] vs. 70 years [53–85]; p

LGMDD2 is a rare form of muscular dystrophy characterized by one of the three heterozygous deletions described within the TNPO3 gene that result in the addition of a 15-amino acid tail in the C-terminus.TNPO3 is involved in the nuclear import of splicing factors and acts as a host cofactor for HIV-1 infection by mechanisms not yet deciphered. Further characterization of the crosstalk between HIV-1 infection and LGMDD2 disease may contribute to a better understanding of both the cellular alterations occurring in LGMDD2 patients and the role of TNPO3 in the HIV-1 cycle. To this regard, transcriptome profiling of PBMCs from LGMDD2 patients carrying the deletion c.2771delA in the TNPO3 gene was compared to healthy controls. A total of 545 differentially expressed genes were detected between LGMDD2 patients and healthy controls, with a high representation of G protein-coupled receptor binding chemokines and metallopeptidases among the most upregulated genes in LGMDD2 patients. Plasma levels of IFN-β and IFN-γ were 4.7- and 2.7-fold higher in LGMDD2 patients, respectively. An increase of 2.3-fold in the expression of the interferon-stimulated gene MxA was observed in activated PBMCs from LGMDD2 patients after ex vivo HIV-1 pseudovirus infection. Thus, the analysis suggests a pro-inflammatory state in LGMDD2 patients also described for other muscular dystrophies, that is characterized by the alteration of IL-17 signaling pathway and the consequent increase of metallopeptidases activity and TNF response. In summary, the increase in interferons and inflammatory mediators suggests an antiviral environment and resistance to HIV-1 infection but that could also impair muscular function in LGMDD2 patients, worsening disease evolution. Biomarkers of disease progression and therapeutic strategies based on these genes and mechanisms should be further investigated for this type of muscular dystrophy.

Little is known about von Economo neurons, which have been described in a subset of mammals and appear to be selectively lost in several human neurological diseases. Here, authors reveal the gene expression profile of these cells and show that they are likely long-distance projection neurons.

Summary: CombiVacS study has demonstrated a strong immune response of the heterologous ChAdOx1-S/BNT162b2 vaccine combination. The primary outcomes of the study were to assess the humoral immune response against SARS-CoV-2, 28 days after a third dose of a mRNA vaccine, in subjects that received a previous prime-boost scheme with ChAdOx1-S/BNT162b2. Secondary outcomes extended the study to 3 and 6 months. The third vaccine dose of mRNA-1273 in naive participants previously vaccinated with ChAdOx1-S/BNT162b2 regimen reached higher neutralizing antibodies titers against the variants of concern Delta and BA.1 lineage of Omicron compared with those receiving a third dose of BNT162b2 at day 28. These differences between BNT162b2 and mRNA-1273 arms were observed against the ancestral variant G614 at day 90. Suboptimal neutralizing response was observed against BQ.1.1, XBB.1.5/XBB.1.9, and JN.1 in a relevant proportion of individuals 180 days after the third dose, even after asymptomatic Omicron breakthrough infections. EudraCT (2021-001978-37); ClinicalTrials.gov (NCT04860739).

Abstract Different phenotypes exhibiting no evidences of disease progression have been described in ART-naïve HIV-1 positive individuals. Long-term non progressors (LTNP) and elite controllers (EC) are low frequent examples of immunological and virological control in HIV-1 positive subjects, respectively. The combination of both phenotypes is even less frequent and studied despite being considered as models of HIV-1 functional cure. A multicenter, prospective study in retrospect including clinical and epidemiological data collected from 313 LTNP of 21 Spanish hospitals was carried out. LTNPs maintaining CD4+ T cell counts over 500 cells/µl and viral loads (VL) under 10,000 copies/mL for at least 10 years in the absence of antiretroviral therapy were followed for a median of 20.8 years (IQR = 15.6–25.5). A 52.1% were considered EC (undetectable VL) and LTNP (EC-LTNP) and a total of 171 (54.8%) and 42 (13.5%) out of the 313 participants maintained LTNP status for at least 20 and 30 years, respectively. EC-LTNP showed lower CD4+ T cell count loss (9.9 vs 24.2 cells/µl/year), higher CD4/CD8 ratio (0.01 vs − 0.09 in ratio), and lesser VL increase (no increase vs 197.2 copies/mL/year) compared with LTNPs with detectable VL (vLTNP). Survival probabilities for all-cause mortality at 30 years from HIV + diagnosis were 0.90 for EC-LTNP and 0.70 for vLTNP (p = 2.0 × 10−3), and EC-LTNP phenotype was the only factor associated with better survival in multivariate analyses (HR = 0.28; 95% CI 0.10–0.79). The probability to preserve LTNP status at 30 years was 0.51 for EC-LTNP and 0.18 for vLTNP (p

ABSTRACT Remdesivir (RDV) was the first antiviral drug approved by the FDA to treat severe coronavirus disease-2019 (COVID-19) patients. RDV inhibits SARS-CoV-2 replication by stalling the non structural protein 12 (nsp12) subunit of the RNA-dependent RNA polymerase (RdRp). No evidence of global widespread RDV-resistance mutations has been reported, however, defining genetic pathways to RDV resistance and determining emergent mutations prior and subsequent antiviral therapy in clinical settings is necessary. This study identified 57/149 (38.3%) patients who did not respond to one course (5-days) (n = 36/111, 32.4%) or prolonged (5 to 20 days) (n = 21/38, 55.3%) RDV therapy by subgenomic RNA detection. Genetic variants in the nsp12 gene were detected in 29/49 (59.2%) non responder patients by Illumina sequencing, including the de novo E83D mutation that emerged in an immunosuppressed patient after receiving 10 + 8 days of RDV, and the L838I detected at baseline and/or after prolonged RDV treatment in 9/49 (18.4%) non responder subjects. Although 3D protein modeling predicted no interference with RDV, the amino acid substitutions detected in the nsp12 involved changes on the electrostatic outer surface and in secondary structures that may alter antiviral response. It is important for health surveillance to study potential mutations associated with drug resistance as well as the benefit of RDV retreatment, especially in immunosuppressed patients and in those with persistent replication. IMPORTANCE This study provides clinical and microbiologic data of an extended population of hospitalized patients for COVID-19 pneumonia who experienced treatment failure, detected by the presence of subgenomic RNA (sgRNA). The genetic variants found in the nsp12 pharmacological target of RDV bring into focus the importance of monitoring emergent mutations, one of the objectives of the World Health Organization (WHO) for health surveillance. These mutations become even more crucial as RDV keeps being prescribed and new molecules are being repurposed for the treatment of COVID-19. The present article offers new perspectives for the clinical management of non responder patients treated and retreated with RDV and emphasizes the need of further research of the benefit of combinatorial therapies and RDV retreatment, especially in immunosuppressed patients with persistent replication after therapy.

Summary: Background: There is no evidence to date on immunogenic response among individuals who participated in clinical trials of COVID-19 experimental vaccines redirected to standard national vaccination regimens. Methods: This multicentre, prospective controlled cohort study included subjects who received a COVID-19 experimental vaccine (CVnCoV)(test group, TG) - and unvaccinated subjects (control group, CG), selected among individuals to be vaccinated according to the Spanish vaccination program. All study subjects received BNT162b2 as a standard national vaccination schedule, except 8 (from CG) who received mRNA-1273 and were excluded from immunogenicity analyses. Anti-RBD antibodies level and neutralising titres (NT50) against G614, Beta, Mu, Delta and Omicron variants were analysed. Reactogenicity was also assessed. Findings: 130 participants (TG:92; CG:38) completed standard vaccination. In TG, median (IQR) of anti-RBD antibodies after first BNT162b2 dose were 10740·0 BAU/mL (4466·0-12500) compared to 29·8 BAU/mL (14·5-47·8) in CG (p

In August 2018, a fatal autochthonous case of Crimean-Congo hemorrhagic fever was confirmed in western Spain. The complete sequence of the viral genome revealed circulation of a new virus because the genotype differs from that of the virus responsible for another case in 2016. Practitioners should be alert to possible new cases.

This article reviews the main discoveries achieved by transcriptomic approaches on HIV controller (HIC) and long-term non-progressor (LTNP) individuals, who are able to suppress HIV replication and maintain high CD4+ T cell levels, respectively, in the absence of antiretroviral therapy. Different studies using high throughput techniques have elucidated multifactorial causes implied in natural control of HIV infection. Genes related to IFN response, calcium metabolism, ribosome biogenesis, among others, are commonly differentially expressed in LTNP/HIC individuals. Additionally, pathways related with activation, survival, proliferation, apoptosis and inflammation, can be deregulated in these individuals. Likewise, recent transcriptomic studies include high-throughput sequencing in specific immune cell subpopulations, finding additional gene expression patterns associated to viral control and/or non-progression in immune cell subsets. Herein, we provide an overview of the main differentially expressed genes and biological routes commonly observed on immune cells involved in HIV infection from HIC and LTNP individuals, analyzing also different technical aspects that could affect the data analysis and the future perspectives and gaps to be addressed in this field.

The effect of emerging SARS-CoV-2 variants on vaccine efficacy is of critical importance. In this study, the potential impact of mutations that facilitate escape from the cytotoxic cellular immune response in these new virus variants for the 551 most abundant HLA class I alleles was analyzed. Computational prediction showed that most of these alleles, that cover >90% of the population, contain enough epitopes without escape mutations in the principal SARS-CoV-2 variants. These data suggest that the cytotoxic cellular immune protection elicited by vaccination is not greatly affected by emerging SARS-CoV-2 variants.

Abstract The elite controller (EC)-long term non-progressor (LTNP) phenotype represent a spontaneous and advantageous model of HIV-1 control in the absence of therapy. The transcriptome of peripheral blood mononuclear cells (PBMCs) collected from EC-LTNPs was sequenced by RNA-Seq and compared with the transcriptomes from other phenotypes of disease progression. The transcript abundance estimation combined with the use of supervised classification algorithms allowed the selection of 20 genes and pseudogenes, mainly involved in interferon-regulated antiviral mechanisms and cell machineries of transcription and translation, as the best predictive genes of disease progression. Differential expression analyses between phenotypes showed an altered calcium homeostasis in EC-LTNPs evidenced by the upregulation of several membrane receptors implicated in calcium-signaling cascades and intracellular calcium-mobilization and by the overrepresentation of NFAT1/Elk-1-binding sites in the promoters of the genes differentially expressed in these individuals. A coordinated upregulation of host genes associated with HIV-1 reverse transcription and viral transcription was also observed in EC-LTNPs –i.e. p21/CDKN1A, TNF, IER3 and GADD45B. We also found an upregulation of ANKRD54 in EC-LTNPs and viremic LTNPs in comparison with typical progressors and a clear alteration of type-I interferon signaling as a consequence of viremia in typical progressors before and after receiving antiretroviral therapy.

Porcine reproductive and respiratory syndrome (PRRS) is considered one of the most relevant diseases of swine. The condition is caused by PRRS virus (PRRSV), an extremely variable virus of the Arteriviridae family. Its heterogeneity can be responsible, at least partially, of the poor cross-protection observed between PRRSV isolates. Neutralizing antibodies (NAs), known to play a role in protection, usually poorly recognize heterologous PRRSV isolates, indicating that most NAs are strain-specific. However, some pigs develop broadly reactive NAs able to recognize a wide range of heterologous isolates. The aim of this study was to determine whether PRRSV isolates that induce broadly reactive NAs as determined in vitro are able to confer a better protection in vivo. For this purpose two in vivo experiments were performed. Initially, 40 pigs were immunized with a PRRSV-1 isolate known to induce broadly reactive NAs and 24 additional pigs were used as controls. On day 70 after immunization, the pigs were divided into eight groups composed by five immunized and three control pigs and exposed to one of the eight different heterologous PRRSV isolates used for the challenge. In the second experiment, the same experimental design was followed but the pigs were immunized with a PRRSV-1 isolate, which is known to generate mostly strain-specific NAs. Virological parameters, specifically viremia and the presence of challenge virus in tonsils, were used to determine protection. In the first experiment, sterilizing immunity was obtained in three groups, prevention of viremia was observed in two additional groups, although the challenge virus was detected occasionally in the tonsils of immunized pigs, and partial protection, understood as a reduction in the frequency of viremia compared with controls, was recorded in the remaining three groups. On the contrary, only partial protection was observed in all groups in the second experiment. The results obtained in this study confirm that PRRSV-1 isolates differ in their ability to induce cross-reactive NAs and, although other components of the immune response might have contributed to protection, pigs with cross-reactive NAs at the time of challenge exhibited better protection, indicating that broadly reactive NAs might play a role in protection against heterologous reinfections.

In Western Europe, the HIV-1 epidemic among men who have sex with men (MSM) is dominated by subtype B. However, recently, other genetic forms have been reported to circulate in this population, as evidenced by their grouping in clusters predominantly comprising European individuals. Here we describe four large HIV-1 non-subtype B clusters spreading among MSM in Spain. Samples were collected in 9 regions. A pol fragment was amplified from plasma RNA or blood-extracted DNA. Phylogenetic analyses were performed via maximum likelihood, including database sequences of the same genetic forms as the identified clusters. Times and locations of the most recent common ancestors (MRCA) of clusters were estimated with a Bayesian method. Five large non-subtype B clusters associated with MSM were identified. The largest one, of F1 subtype, was reported previously. The other four were of CRF02_AG (CRF02_1; n = 115) and subtypes A1 (A1_1; n = 66), F1 (F1_3; n = 36), and C (C_7; n = 17). Most individuals belonging to them had been diagnosed of HIV-1 infection in the last 10 years. Each cluster comprised viruses from 3 to 8 Spanish regions and also comprised or was related to viruses from other countries: CRF02_1 comprised a Japanese subcluster and viruses from 8 other countries from Western Europe, Asia, and South America; A1_1 comprised viruses from Portugal, United Kingom, and United States, and was related to the A1 strain circulating in Greece, Albania and Cyprus; F1_3 was related to viruses from Romania; and C_7 comprised viruses from Portugal and was related to a virus from Mozambique. A subcluster within CRF02_1 was associated with heterosexual transmission. Near full-length genomes of each cluster were of uniform genetic form. Times of MRCAs of CRF02_1, A1_1, F1_3, and C_7 were estimated around 1986, 1989, 2013, and 1983, respectively. MRCA locations for CRF02_1 and A1_1 were uncertain (however initial expansions in Spain in Madrid and Vigo, respectively, were estimated) and were most probable in Bilbao, Spain, for F1_3 and Portugal for C_7. These results show that the HIV-1 epidemic among MSM in Spain is becoming increasingly diverse through the expansion of diverse non-subtype B clusters, comprising or related to viruses circulating in other countries.

Systems vaccinology has seldomly been used in therapeutic HIV-1 vaccine research. Our aim was to identify early gene ‘signatures’ that predicted virus load control after analytical therapy interruption (ATI) in participants of a dendritic cell-based HIV-1 vaccine trial (DCV2). mRNA and miRNA were extracted from frozen post-vaccination PBMC samples; gene expression was determined by microarray method. In gene set enrichment analysis, responders showed an up-regulation of 14 gene sets (TNF-alpha/NFkB pathway, inflammatory response, the complement system, Il6 and Il2 JAK-STAT signaling, among others) and a down-regulation of 7 gene sets (such as E2F targets or interferon alpha response). The expression of genes regulated by three (miR-223-3p, miR-1183 and miR-8063) of the 9 differentially expressed miRNAs was significantly down-regulated in responders. The deregulation of certain gene sets related to inflammatory processes seems fundamental for viral control, and certain miRNAs may be important in fine-tuning these processes.

Therapeutic vaccines based on dendritic cells offer a good approach to HIV-specific T-cell responses and partial control of the viral load after antiretroviral therapy interruption. The aim of the present study was to identify mRNA expression profiles and to assess the impact of the gut microbiome composition for predicting the viral load control after antiretroviral therapy interruption. We enrolled 29 patients to receive either placebo or a monocyte-derived dendritic cell vaccine. Patients with a decrease in their viral load of >0.5 log10 copies/mL by 12 weeks after antiretroviral therapy interruption were considered responders. In total, 66 genes were considered differentially expressed between responders and non-responders. Enrichment analysis revealed several upregulated pathways involved in the host defense response to a virus via the type I interferon signaling pathway. Regarding the gut microbiota, responders showed enriched levels of Bacteroidetes (p < 0.005) and Verrucomicrobia (p = 0.017), while non-responders were enriched with Tenericutes (p = 0.049) and Actinobacteria (p < 0.005). We also found important differences at the genus level. However, we did not discover any effect of the dendritic cell vaccine on the transcriptome or the gut microbiota. An alternative analysis did characterize that the microbiota from responders were associated with the metabolic production of short-chain fatty acids, which are key metabolites in the regulation of intestinal homeostasis. The evidence now consistently shows that short-chain fatty acid depletion occurs in HIV-infected individuals receiving antiretroviral treatment.

Certain host genetic variants, especially in the human leucocyte antigen (HLA) region, are associated with different progression of HIV-1-induced diseases and AIDS. Long term non progressors (LTNP) represent only the 2% of infected patients but are especially relevant because of their efficient HIV control. In this work we present a global analysis of genetic data in the large national multicenter cohort of Spanish LTNP, which is compared with seronegative individuals and HIV-positive patients. We have analyzed whether several single-nucleotide polymorphisms (SNPs) including in key genes and certain HLA-A and B alleles could be associated with a specific HIV phenotype. A total of 846 individuals, 398 HIV-1-positive patients (213 typical progressors, 55 AIDS patients, and 130 LTNPs) and 448 HIV-negative controls, were genotyped for 15 polymorphisms and HLA-A and B alleles. Significant differences in the allele frequencies among the studied populations identified 16 LTNP-associated genetic factors, 5 of which were defined for the first time as related to LTNP phenotype: the protective effect of HLA-B39, and the detrimental impact of HLA-B18, -A24, -B08 and -A29. The remaining eleven polymorphisms confirmed previous publications, including the protective alleles HLA-B57, rs2395029 (HCP5), HLA bw4 homozygosity, HLA-B52, HLA-B27, CCR2 V64I, rs9264942 (HLA-C) and HLA-A03; and the risk allele HLA bw6 homozygosity. Notably, individual Spanish HIV-negative individuals had an average of 0.12 protective HLA alleles and SNPs, compared with an average of 1.43 protective alleles per LTNP patient, strongly suggesting positive selection of LTNP. Finally, stratification of LTNP according to viral load showed a proportional relationship between the frequency of protective alleles with control of viral load. Interestingly, no differences in the frequency of protection/risk polymorphisms were found between elite controllers and LTNPs maintaining viral loads

HIV-1 induces changes in the miRNA expression profile of infected CD4+ T cells that could improve viral replication. HIV-1 regulator Tat modifies the cellular gene expression and has been appointed as an RNA silencing suppressor. Tat is a 101-residue protein codified by two exons that regulates the elongation of viral transcripts. The first exon of Tat (amino acids 1-72) forms the transcriptionally active protein Tat72, but the presence of the second exon (amino acids 73-101) results in a more competent regulatory protein (Tat101) with additional functions. Intracellular, full-length Tat101 induces functional and morphological changes in CD4+ T cells that contribute to HIV-1 pathogenesis such as delay in T-cell proliferation and protection against FasL-mediated apoptosis. But the precise mechanism by which Tat produces these changes remains unknown. We analyzed how the stable expression of intracellular Tat101 and Tat72 modified the miRNA expression profile in Jurkat cells and if this correlated with changes in apoptotic pathways and cell cycle observed in Tat-expressing cells. Specifically, the enhanced expression of hsa-miR-21 and hsa-miR-222 in Jurkat-Tat101 cells was associated with the reduced expression of target mRNAs encoding proteins related to apoptosis and cell cycle such as PTEN, PDCD4 and CDKN1B. We developed Jurkat cells with stable expression of hsa-miR-21 or hsa-miR-222 and observed a similar pattern to Jurkat-Tat101 in resistance to FasL-mediated apoptosis, cell cycle arrest in G2/M and altered cell morphology. Consequently, upregulation of hsa-miR-21 and hsa-miR-222 by Tat may contribute to protect against apoptosis and to anergy observed in HIV-infected CD4+ T cells.

HIV-1 RNAs are generated through a complex splicing mechanism, resulting in a great diversity of transcripts, which are classified in three major categories: unspliced, singly spliced (SS), and doubly spliced (DS). Knowledge on HIV-1 RNA splicing in vivo and by non-subtype B viruses is scarce. Here we analyze HIV-1 RNA splice site usage in CD4+CD25+ lymphocytes from HIV-1-infected individuals through pyrosequencing. HIV-1 DS and SS RNAs were amplified by RT-PCR in 19 and 12 samples, respectively. 13,108 sequences from HIV-1 spliced RNAs, derived from viruses of five subtypes (A, B, C, F, G), were identified. In four samples, three of non-B subtypes, five 3' splice sites (3'ss) mapping to unreported positions in the HIV-1 genome were identified. Two, designated A4i and A4j, were used in 22% and 25% of rev RNAs in two viruses of subtypes B and A, respectively. Given their close proximity (one or two nucleotides) to A4c and A4d, respectively, they could be viewed as variants of these sites. Three 3'ss, designated A7g, A7h, and A7i, located 20, 32, and 18 nucleotides downstream of A7, respectively, were identified in a subtype C (A7g, A7h) and a subtype G (A7i) viruses, each in around 2% of nef RNAs. The new splice sites or variants of splice sites were associated with the usual sequence features of 3'ss. Usage of unusual 3'ss A4d, A4e, A5a, A7a, and A7b was also detected. A4f, previously identified in two subtype C viruses, was preferentially used by rev RNAs of a subtype C virus. These results highlight the great diversity of in vivo splice site usage by HIV-1 RNAs. The fact that four of five newly identified splice sites or variants of splice sites were detected in non-subtype B viruses allows anticipating an even greater diversity of HIV-1 splice site usage than currently known.

The cyst-forming protozoan parasite Neosporacaninum is one of the main causes of bovine abortion worldwide and is of great economic importance in the cattle industry. Recent studies have revealed extensive genetic variation among N. caninum isolates based on microsatellite sequences (MSs). MSs may be suitable molecular markers for inferring the diversity of parasite populations, molecular epidemiology and the basis for phenotypic variations in N. caninum, which have been poorly defined. In this study, we evaluated nine MS markers using a panel of 11 N. caninum-derived reference isolates from around the world and 96 N. caninum bovine clinical samples and one ovine clinical sample collected from four countries on two continents, including Spain, Argentina, Germany and Scotland, over a 10-year period. These markers were used as molecular tools to investigate the genetic diversity, geographic distribution and population structure of N. caninum. Multilocus microsatellite genotyping based on 7 loci demonstrated high levels of genetic diversity in the samples from all of the different countries, with 96 microsatellite multilocus genotypes (MLGs) identified from 108 N. caninum samples. Geographic sub-structuring was present in the country populations according to pairwise F(ST). Principal component analysis (PCA) and Neighbor Joining tree topologies also suggested MLG segregation partially associated with geographical origin. An analysis of the MLG relationships, using eBURST, confirmed that the close genetic relationship observed between the Spanish and Argentinean populations may be the result of parasite migration (i.e., the introduction of novel MLGs from Spain to South America) due to cattle movement. The eBURST relationships also revealed genetically different clusters associated with the abortion. The presence of linkage disequilibrium, the co-existence of specific MLGs to individual farms and eBURST MLG relationships suggest a predominant clonal propagation for Spanish N. caninum MLGs in cattle.