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Almost two decades ago, in addition to a compulsory M. gallisepticum (Mg) monitoring programme of breeding stock based on European Union regulations, the Dutch poultry industry added national regulations to further reduce the Mg prevalence in Dutch commercial poultry. Currently, all commercial chicken and turkey flocks except broilers are monitored for Mg. All breeding flocks on a farm where one or more flocks tested Mg positive are culled. Mg positive layer pullets are channelled and layer pullets placed on Mg positive multi-age farms are vaccinated. The monitoring data obtained were analysed covering a period of 17 years. Moreover, 31 Dutch Mg isolates from the same period were analysed by multilocus sequence typing (MLST) and compared to available PubMLST data. The results show that in breeding stock the seroprevalence decreased from 1.6% to 0.0%, in commercial layers from 6.3% to 1.9%, and in meat turkeys from 17.6% to 2.4%. The MLST results showed the presence of closely related and identical sequence types (STs) within the different Dutch poultry types. Similar STs were found in Northern and Southern Europe only. The results show a fast decline in the Mg prevalence since 2001, although in layers the Mg prevalence has stabilized and suggests backyard poultry might pose a risk for commercial poultry. The need for Mg control across poultry sectors and in trade was confirmed by the similarity in STs found in different types of poultry and regions. These results from the Dutch poultry industry can be extrapolated to Mg control in general. [ABSTRACT FROM AUTHOR]

Intestinal disease has a major impact on the broiler industry due to economic and welfare reasons. Intestinal disease might occur due to a large number of reasons varying from well-defined pathogens to non-specific enteritis and complex syndromes. However, knowledge about the nature of intestinal disease and presence of enteric viruses in the Dutch broiler industry is largely absent. Therefore, a large-scale field study, in which 98 broiler flocks from 86 farms were sampled weekly, was started to assess the prevalence of histopathological lesions in the jejunum, a number of enterotropic viruses by real-time quantitative reverse transcriptase PCR (RT-qPCR) and coccidia by lesion scoring. Histopathological lesions indicative of intestinal disease were found in all flocks examined. The pathogens investigated were chicken astrovirus (99% of flocks positive), avian nephritis virus 3 (100%), rotavirus A (95%), rotavirus D (52%), reovirus (100%), Eimeria acervulina (94%), E. maxima (49%) and E. tenella (40%). The enteric viruses were more prevalent in the first weeks of the growing period, while coccidiosis was more frequently found at 4 and 5 weeks of age. The abundant presence of the enteric viruses and enteric disorders stresses the need to elucidate the role of these viruses in intestinal disease. Furthermore, the high prevalence of coccidiosis despite the use of anticoccidials shows that the current coccidial management programmes might be insufficient in controlling this disease. [ABSTRACT FROM AUTHOR]

Beside biosecurity, vaccination is important for Mycoplasma synoviae (MS) control as it has been shown to contribute to the reduction of economic impact and, experimentally, also lessens horizontal transmission. In this study, the effect of MS live vaccination on horizontal transmission was quantified under field conditions by analysing 4-year MS monitoring data from non-MS-vaccinated broiler and layer breeders and MS-vaccinated broiler breeders with good biosecurity in single-age housing systems. Flocks were monitored at 20 and 30 weeks of age and every 12 weeks thereafter. At every sampling, 60 blood samples or 24 tracheal swabs were tested using rapid plate agglutination test and ELISA serially or MS DIVA PCR, respectively. The MS incidence rate was calculated and the association with vaccination was analysed by logistic regression. The average MS incidence rate per 1000 weeks was 11.6 cases for non-MS-vaccinated broiler breeders and decreased from 29.6 to 5.6 cases with successive vaccinated production cycles. In non-MS-vaccinated layer breeders it was 3.6. A significant negative association with MS incidence was found after vaccinating four to six successive production cycles compared to non-MS-vaccinated or only one production cycle vaccinated breeders (odds ratio (OR) = 0.23, P  = 0.05 & OR = 0.12, P  = 0.01, respectively). A significant negative association with MS in non-MS-vaccinated layer breeders (OR = 0.29, P  = 0.00) was observed compared to non-MS-vaccinated broiler breeders, possibly due to more controlled contact structures within the layer breeder industry. The results suggest that vaccination and control of contacts contribute to the reduction of between-farm MS transmission.

Research Highlights: Cerebral granulomas are associated with nervous signs in Salmonella Pullorum outbreak.Bone marrow is also a recommended tissue for isolation of Salmonella Pullorum.Rapid plate agglutination test detects Pullorum antibodies in a vaccinated flock.Phylogenetic analysis showed clonality of isolates within the outbreak.

In Europe, monitoring of breeding stock for Salmonella Pullorum (SP) or Salmonell a Gallinarum (SG) infections is compulsory at the point of lay. Vaccinations against Salmonella Enteritidis (SE) and Salmonella Typhimurium (ST) are increasingly administered in Europe. These vaccines might induce cross-reactions in the rapid plate agglutination (RPA) SP/SG test due to shared O-antigens, possibly resulting in a lower test specificity. The extent to which the specificity of SP/SG serological tests is influenced by SE and/or ST vaccinations in the field has not been reported. In this paper, we report the diagnostic and flock specificity of the commercially available RPA SP/SG test using 1:2-1:16 serum dilutions on four panels of sera: SPF sera, field sera from flocks of varying age and SE/ST vaccination status, and reference sera from an international proficiency testing scheme. The results showed that the use of live SE/ST vaccines did not influence the specificity of the RPA SP/SG test. Inactivated vaccines showed a drop of the diagnostic specificity to 96.54% and a flock specificity of 34.1% when the 1:2 serum dilution was used. The 1:8 serum dilution showed a diagnostic specificity of 99.41% and a flock specificity of 86.4%. In conclusion, the use of SE/ST vaccines has either no effect or a modest effect on the specificity of the RPA SP/SG test used to monitor flocks. The main factors are the type of vaccine, and the serum dilution used for testing and a cut-off.

Mycoplasma synoviae is one of the economically most significant avian Mycoplasma species. It can cause great financial losses to the poultry industry by inducing respiratory diseases, infectious synovitis, or eggshell apex abnormalities. There are different approaches to control M. synoviae infection. Although antimicrobial therapy cannot replace long-term solutions, like eradication and vaccination, this strategy can be effective in the short term, as adequate antibiotic treatment can relieve economic losses through the attenuation of clinical signs and reduction of transmission. Using broth microdilution method, minimal inhibitory concentration (MIC) values to fourteen antibiotics related to eight antimicrobial groups were determined in 96 M. synoviae strains. Whole genome sequencing and sequence analysis revealed mutations potentially associated with decreased susceptibility to fluoroquinolones, macrolides and lincomycin. Molecular markers responsible for the high MICs to fluoroquinolones were found in the gyrA, gyrB, parC and parE genes. Besides, single nucleotide polymorphisms identified in genes encoding the 23S rRNA were found to be responsible for high MICs to the 50S inhibitor macrolides and lincomycin, while amino acid change in the 50S ribosomal protein L22 could be associated with decreased susceptibility to macrolides. The revealed mutations can contribute to the extension of knowledge about the genetic background of antibiotic resistance in M. synoviae. Moreover, the explored potentially resistance-related mutations may serve as targets for molecular biological assays providing data of antibiotic susceptibility prior to the laborious and time-consuming isolation of M. synoviae strains., (Copyright © 2020 The Author(s). Published by Elsevier B.V. All rights reserved.)

To protect layers, breeders and grandparents against damage by infectious bronchitis virus infections during the laying period, vaccination using live priming followed by a boost with inactivated IB vaccine is commonly used. For many IB variants, homologous live vaccines are not available for priming. Very little is known about the efficacy of priming with heterologous live IB vaccines (or combination of live IB vaccines) to induce broad IB protection in long-living chickens. In this study, the protection levels induced by vaccination programmes with only heterologous live priming by a Massachusetts vaccine and a 4/91 vaccine, only a multivalent inactivated vaccine that contained D1466 antigen and a combination of both, against a D1466 challenge were compared. The infection with infectious bronchitis virus D1466, a genotype II, lineage 1 virus, was able to cause serious damage to the unvaccinated laying hens resulting in respiratory signs, a long-lasting drop in egg production and loss of egg quality. All three vaccination programmes induced significant levels of protection against challenge with a pathogenic D1466 strain. Overall, the vaccination programme using the broad heterologous live priming and the inactivated vaccine provided high protection against the combination of egg drop and loss of egg quality. The results showed that this combination of heterologous live vaccines was able to increase the efficacy of the inactivated infectious bronchitis virus vaccine despite the very low antigenic relationship of both live vaccines with the challenge strain.

No recent information is available on the specificity of current M. synoviae (Ms) and M. gallisepticum (Mg) serological tests. In this study the performance of a currently available Mg and Ms Rapid Plate Agglutination (RPA) test, and three Mg, three Ms and three Mg/Ms combination ELISAs were evaluated on SPF sera that were obtained from days (D) 0-28 after M. gallinarum , M. imitans or M. gallinaceum inoculation, after sham inoculation and without inoculation. Tracheal swabs for mycoplasma culture were obtained before inoculation (D0), 7 and 28 days post inoculation (d.p.i.) in all groups except the sham inoculated group. The different mycoplasma species colonized well. In the early stage after inoculation (7-14 d.p.i.) with heterologous mycoplasma species, the specificity varied from 85% to 100% in the Mg RPA test and from 70% to 85% in the Ms RPA test. The specificity of both Mg and Ms RPA test was 100% in the sham inoculated samples and ruled out the effect of sham medium. In the late stage (21-28 d.p.i.) specificity was 100% for both RPA tests. The test specificity was 100% for seven ELISAs except for two combination ELISAs where a specificity of 95% was found in the late stage after inoculation. However, this was not significantly different from the specificity of all other tests in the late stage of these groups. These results show that it is not advisable to establish Mg and Ms seromonitoring programmes on the Mg and Ms RPA test alone as other mycoplasma species frequently occur in poultry.

To gain more insight into the within flock transmission of Histomonas meleagridis, the shedding of parasites was quantified by a newly developed real-time quantitative (q)PCR and the basic reproduction number (R0) and the mean number of secondary infections per infectious bird per day in a susceptible population (β) of H. meleagridis in the absence of heterakis were assessed. Forty turkeys were divided into two groups of 10 and 30 birds at 14 days of age. Birds of the first group were inoculated with 200,000 histomonads each, the second group served as a susceptible contact group. Cloacal swabs were taken at -1, 1, 4, 7, 9, 11, 14, 18 and 21 days post inoculation (p.i.) to assess the shedding of the parasite by the qPCR (detection limit 330 histomonads/ml droppings). The experiment ended at 28 days p.i. Mortality was 100% in the inoculated birds and started at day 12 p.i., while in the contacts, it was 83% and started at 16 days p.i. Shedding started 1 day after the inoculation in both groups. The mean shedding levels (and 95% CI) expressed as parasite equivalents per gram cloacal content on a log10 scale in the inoculated, contact birds that died and contact birds alive were 2.0 (1.6-2.4), 1.6 (1.4-1.9) and 1.2 (0.5-2.0), respectively. Birds that died shed histomonas more often and were infectious for 13.4 days; in contrast, those that recovered were infectious for 5.7 days. R0 was estimated to be 8.4 and β 0.70. Simulations made with the parameters obtained were in agreement with the experimental results, confirming their validity.