Blood B Cell Depletion Reflects Immunosuppression Induced by Live-Attenuated Infectious Bursal Disease Vaccines

Immunosuppression in poultry production is a recurrent problem worldwide, and one of the major viral immunosuppressive agents is Infectious Bursal Disease Virus (IBDV). IBDV infections are mostly controlled by using live-attenuated vaccines. Live-attenuated Infectious Bursal Disease (IBD) vaccine candidates are classified as “mild,” “intermediate,” “intermediate-plus” or “hot” based on their residual immunosuppressive properties. The immunosuppression protocol described by the European Pharmacopoeia (Ph. Eur.) uses a lethal Newcastle Disease Virus (NDV) infectious challenge to measure the interference of a given IBDV vaccine candidate on NDV vaccine immune response. A Ph. Eur.-derived protocol was thus implemented to quantify immunosuppression induced by one mild, two intermediate, and four intermediate-plus live-attenuated IBD vaccines as well as a pathogenic viral strain. This protocol confirmed the respective immunosuppressive properties of those vaccines and virus. In the search for a more ethical alternative to Ph. Eur.-based protocols, two strategies were explored. First, ex vivo viral replication of those vaccines and the pathogenic strain in stimulated chicken primary bursal cells was assessed. Replication levels were not strictly correlated to immunosuppression observed in vivo. Second, changes in blood leukocyte counts in chicks were monitored using a Ph. Eur. - type protocol prior to lethal NDV challenge. In case of intermediate-plus vaccines, the drop in B cells counts was more severe. Counting blood B cells may thus represent a highly quantitative, faster, and ethical strategy than NDV challenge to assess the immunosuppression induced in chickens by live-attenuated IBD vaccines

Infectious Bronchitis Coronavirus: Genome Evolution in Vaccinated and Non-Vaccinated SPF Chickens

Infectious Bronchitis virus (IBV) continues to cause significant economic losses for the chicken industry despite the use of many live IBV vaccines around the world. Several authors have suggested that vaccine-induced partial protection may contribute to the emergence of new IBV strains. In order to study this hypothesis, three passages of a challenge IBV were made in SPF chickens sham inoculated or vaccinated at day of age using a live vaccine heterologous to the challenge virus. All birds that were challenged with vaccine heterologous virus were positive for viral RNA. NGS analysis of viral RNA in the unvaccinated group showed a rapid selection of seven genetic variants, finally modifying the consensus genome of the viral population. Among them, five were non-synonymous, modifying one position in NSP 8, one in NSP 13, and three in the Spike protein. In the vaccinated group, one genetic variant was selected over the three passages. This synonymous modification was absent from the unvaccinated group. Under these conditions, the genome population of an IBV challenge virus evolved rapidly in both heterologous vaccinated and non-vaccinated birds, while the genetic changes that were selected and the locations of these were very different between the two groups

Research Note: Detection of Avian metapneumovirus subgroup C specific antibodies in a mallard flock in Italy

none5siAvian metapneumovirus (aMPV) is a viral pathogen that causes respiratory signs and drops in egg production most notably in turkeys but also affects chickens, ducks and other species. Four subgroups (aMPV-A, -B, -C and -D) have been characterized to date, which differ genetically, antigenically and in terms of geographic distribution and host range. Despite the rising awareness towards aMPV, many aspects of its epidemiology are still poorly understood. In this pilot study, a serological survey was carried out to assess the possible circulation of subgroups A, B, and C in intensively raised ducks in Northern Italy. A total of 220 sera from 10 Pekin duck flocks and one mallard flock were collected at slaughter and tested by subgroup-specific aMPV-A, B, and C indirect ELISA assays. None of the tested birds had been vaccinated against aMPV and no symptoms had been reported. No aMPV-A, B or C antibodies were detected in any bird of the Pekin duck flocks, whereas the entire mallard flock tested positive for aMPV-C antibodies. This is the first report of aMPV-C antibodies in ducks in Italy, where only aMPV-B has been reported to circulate in recent years. Further research efforts will be targeted towards the screening of a larger panel of samples, in the hope of obtaining positive samples from which full length genome sequences and infectious viruses can be isolated for virus characterization. Finally, the demonstration of aMPV-C specific antibodies in the serum of all sampled mallards indirectly suggests that this species is readily infected by aMPV-C and supports a possible role of wild anatids as a transmission vector of the virus.noneLegnardi, Matteo; Allée, Chantal; Franzo, Giovanni; Cecchinato, Mattia; Brown, PaulLegnardi, Matteo; Allée, Chantal; Franzo, Giovanni; Cecchinato, Mattia; Brown, Pau

Transmission Kinetics and histopathology induced by European Turkey Coronavirus during experimental infection of specific pathogen free turkeys

Numerous viruses, mostly in mixed infections, have been associated worldwide with poult enteritis complex (PEC). In 2008 a coronavirus (Fr-TCoV 080385d) was isolated in France from turkey poults exhibiting clinical signs compatible with this syndrome. In the present study, the median infectious dose (ID50 ), transmission kinetics and pathogenicity of Fr-TCoV were investigated in 10-day-old SPF turkeys. Results revealed a titre of 104.88 ID50 /ml with 1 ID50 /ml being beyond the limit of genome detection using a well-characterized qRT-PCR for avian coronaviruses. Horizontal transmission of the virus via the airborne route was not observed however, via the oro-faecal route this proved to be extremely rapid (one infectious individual infecting another every 2.5 hr) and infectious virus was excreted for at least 6 weeks in several birds. Histological examination of different zones of the intestinal tract of the Fr-TCoV-infected turkeys showed that the virus had a preference for the lower part of the intestinal tract with an abundance of viral antigen being present in epithelial cells of the ileum, caecum and bursa of Fabricius. Viral antigen was also detected in dendritic cells, monocytes and macrophages in these areas, which may indicate a potential for Fr-TCoV to replicate in antigen-presenting cells. Together these results highlight the importance of good sanitary practices in turkey farms to avoid introducing minute amounts of virus that could suffice to initiate an outbreak, and the need to consider that infected individuals may still be infectious long after a clinical episode, to avoid virus dissemination through the movements of apparently recovered birds

Infectious Bronchitis Coronavirus: Genome Evolution in Vaccinated and Non-Vaccinated SPF Chickens

This research was funded by the “Agence National de Sécurité Sanitaire, de l’Environnement et du travail” (ANSES) and the “Conseil Région Bretagne” (code of convention: 180019)International audienceInfectious Bronchitis virus (IBV) continues to cause significant economic losses for the chicken industry despite the use of many live IBV vaccines around the world. Several authors have suggested that vaccine-induced partial protection may contribute to the emergence of new IBV strains. In order to study this hypothesis, three passages of a challenge IBV were made in SPF chickens sham inoculated or vaccinated at day of age using a live vaccine heterologous to the challenge virus. All birds that were challenged with vaccine heterologous virus were positive for viral RNA. NGS analysis of viral RNA in the unvaccinated group showed a rapid selection of seven genetic variants, finally modifying the consensus genome of the viral population. Among them, five were non-synonymous, modifying one position in NSP 8, one in NSP 13, and three in the Spike protein. In the vaccinated group, one genetic variant was selected over the three passages. This synonymous modification was absent from the unvaccinated group. Under these conditions, the genome population of an IBV challenge virus evolved rapidly in both heterologous vaccinated and non-vaccinated birds, while the genetic changes that were selected and the locations of these were very different between the two groups

Amino acid comparisons of the phospoprotein ORF of AMPV-A, B, C and D and HMPV subgroups A and B.

<p>A region resposible for the tetramerization of the P protein is shown together with a molecular recognition element (MoRE). Grey box represents a highly conserved region in MPVs in the MoRE. *end of protein.</p

Genetic relationships between previously published MPV genome sequences and the full length sequences of Fr-AMPV-C (•) and D (♦).

<p>The tree was constructed as described in the text using the neighbor-joining method. Percentages at branch points represent the number of times the group to the right of that branch point occurred among 1000 trees generated by bootstrap from the original alignment.</p

Amino acid comparisons of the fusion ORF of AMPV-A, B, C and D and HMPV subgroups A and B. Previously identified biologicaly important domains are labled and underlined.

<p>Diamonds indicate conserved cysteine residues. Open boxes highlight other domains discused in the relevent paragraph. Cleavage site (Clv) and integrin binding domain (Ibd). *end of protein.</p

Amino acid comparisons of the nucleocapsid ORF of AMPV-A, B, C and D and HMPV subgroups A and B.

<p>Positions 44 and 137 were specific to Fr-AMPV-C. Grey shaded boxes represent four highly conserved regions across all MPVs. Boxes A, B and C are regions that have been reported to be conserved amongst pneumoviruses (Barr et al 1991). In metapneumoviruses domains B and C appear to be extended creating one single larger domain (B/C). *end of protein.</p