Bursa atrophy at 28 days old caused by variant infectious bursal disease virus has a negative economic impact on broiler farms in Japan.

Infectious bursal disease (IBD), caused by IBD virus (IBDV), is highly contagious, immunosuppressive and causes a negative economic impact on poultry industry. IBDV-vaccinated broiler farms at south Kyushu, Japan had a bursa-to-bodyweight ratio (BB ratio) reduction at 28 days (d) old, followed by high mortality 30 d later. We analysed the influence of the IBDV on atrophy of the bursa of fabricius (BF) and the subsequent mortality after 30 d. Ten broilers were sampled at each timepoint from the farm with high mortality at 21, 25, 28 and 35 d. A second flock from the same farm was sampled at 14, 21, 25, 28, 35 and 42 d. IBDV was detected in BF samples at 25, 28 and 35 d and at 21, 25, 28 and 35 d in the first and second flocks, respectively, using immunohistochemical staining and RT-PCR. IBDV isolates from both flocks were closely related to the China KM523643 strain. Histopathology and TUNEL assay indicated apoptosis, severe lymphoid depletion, vacuoles within follicles, lymphoid follicle atrophy and fibrosis in the BF. We observed 75% of the polyserositis and 10% of the airsacculitis at 30 D in dead broilers. The antigenic variant IBDV infection was appeared to be the main influencing factor on BF atrophy and BB ratio reduction in the broilers. High mortality in the broilers after 30 d could be due to secondary infection. The disease caused by IBDV had a negative economic impact in the farm. RESEARCH HIGHLIGHTS New variant IBDV caused bursa atrophy and reduced BB ratio in 28-day-old broilers. After vIBDV had infected broilers, at 21 days old they became immunosuppressed. High mortality at 30 days old in broilers was due to secondary infection. New vIBDV has a negative economic impact on broiler farms in Japan.

Identification and assessment of virulence of a natural reassortant of infectious bursal disease virus.

Infectious bursal disease virus (IBDV) is one of the most important immunosuppressive viral agents in poultry production. Prophylactic vaccinations of chicken flocks are the primary tool for disease control. Widely used immunoprophylaxis can, however, provide high pressure which contributes to the genetic diversification of circulating viruses, e.g. through reassortment of genome segments. We report the genetic and phenotypic characterization of a field reassortant IBDV (designated as Bpop/03) that acquired segment A from very virulent IBDV and segment B from classical attenuated D78-like IBDV. Despite the mosaic genetic make-up, the virus caused high mortality (80%) in experimentally infected SPF chickens and induced lesions typical of the acute form of IBD. The in vivo study results are in contrast with the foregoing experimental investigations in which the natural reassortants exhibited an intermediate pathotype, and underline the complex nature of IBDV virulence.

A 5-year study of the incidence and economic impact of variant infectious bursal disease viruses on broiler production in Saskatchewan, Canada.

While the prevalence of infectious bursal disease virus (IBDV) on chicken farms in some provinces of Canada has been documented, the economic impact of variant IBDV infection on the broiler chicken industry in Saskatchewan has not. The objectives of this study were to identify the variant strains of IBDV circulating on Saskatchewan chicken farms and evaluate their economic impact on broiler production. Infection due to IBDV was detected in 43% of Saskatchewan chicken farms, with variant strains detected in infected birds closely related predominantly to NC171, 586, and Delaware-E. Infected flocks showed an IBDV antibody titer of 4236 geometric mean (GM), whereas an antibody titer of 157 GM was measured in uninfected flocks. Infected flocks had very low (0.06) bursa-to-body-weight (BBW) ratio (an indicator of immunity) compared to high BBW ratio (0.17) in uninfected flocks, which suggests a significant immunosuppression in the former. Flocks positive for IBDV had mean mortality of 8.6% and mean condemnation of 1.5%. In contrast, mean mortality in uninfected flocks was 6.1% and mean condemnation was 1.1%. The live market weight per grow area at 37 d of age was 29.3 kg/m2 in infected flocks and 34.0 kg/m2 in flocks without IBDV infection. Flock mortality and condemnation rate were positively correlated with IBDV infection, whereas low BBW ratio was inversely correlated, as expected. Overall, IBDV-infected flocks had higher mortality, bursal atrophy, poorer feed conversion ratio (FCR), and decreased meat production. Our data suggest that the broiler chicken industry in Saskatchewan loses 3.9 million kilograms of meat production per year due to variant IBDV strains.

Bien que la prévalence du virus de la maladie infectieuse de la bourse (VMIB) sur les fermes de poulets dans quelques provinces canadiennes ait été documentée, l'impact économique d'infections par des variants du VMIB sur l'industrie du poulet à griller en Saskatchewan ne l'est pas. Les objectifs de la présente étude étaient d'identifier les souches variantes du VMIB circulant au sein des fermes de poulet de la Saskatchewan et d'évaluer leur impact économique sur la production de poulets à griller. L'infection due au VMIB a été détectée sur 43 % des fermes de poulet de la Saskatchewan, avec des souches variantes détectées chez des oiseaux infectés étant fortement apparentées en prédominance aux souches NC171, 586, et Delaware-E. Les troupeaux infectés présentaient une moyenne géométrique (MG) des titres d'anticorps contre le VMIB de 4236, alors que la MG des titres d'anticorps des oiseaux provenant de troupeaux non-infectés était de 157. Les troupeaux infectés avaient un très faible ratio (0,06) du poids bourse-poids corporel (BPC) (un indicateur de l'immunité) comparativement au ratio BPC élevé (0,17) dans les troupeaux non-infectés, ce qui suggère une immunosuppression significative dans les troupeaux infectés. Les troupeaux positifs au VMIB avaient un taux de mortalité moyen de 8,6 % et un taux de condamnation moyen de 1,5 %. À l'opposé, dans les troupeaux non-infectés le taux de mortalité moyen était de 6,1 % et le taux de condamnation moyen de 1,1 %. Le poids vif de marché à 37 j d'âge par surface de croissance était de 29,3 kg/m2 dans les troupeaux infectés et de 34,0 kg/m2 dans les troupeaux sans infection par VMIB. La mortalité dans le troupeau et le taux de condamnation étaient corrélés positivement avec l'infection par VMIB, alors qu'un faible ratio BPC était corrélé, tel qu'attendu, de manière inverse. De manière générale, les troupeaux infectés par le VMIB présentaient une mortalité plus élevée, une atrophie de la bourse, un mauvais ratio de conversion alimentaire, et une production de viande réduite. Nos données suggèrent que l'industrie du poulet à griller en Saskatchewan perd annuellement 3,9 millions de kilogrammes de production de viande à cause des souches variantes du VMIB.(Traduit par Docteur Serge Messier).

Development, standardization and assessment of PCR systems for purity testing of avian viral vaccines.

The European Pharmacopoeia (Ph. Eur.) requires avian viral vaccines to be free of adventitious agents. Purity testing is an essential quality requirement of immunological veterinary medicinal products (IVMPs) and testing for extraneous agents includes monitoring for many different viruses. Conventional virus detection methods include serology or virus culture, however, molecular tests have become a valid alternative testing method. Nucleic acid testing (NAT) is fast, highly sensitive and has a higher degree of discrimination than conventional approaches. These advantages have led to the development and standardization of polymerase chain reaction (PCR) assays for the detection of avian leucosis virus, avian orthoreovirus, infectious bursal disease virus, infectious bronchitis virus, Newcastle disease virus, infectious laryngotracheitis virus, influenza A virus, Marek's disease virus, turkey rhinotracheitis virus, egg drop syndrome virus, chicken anaemia virus, avian adenovirus and avian encephalomyelitis virus. This paper reviews the development, standardization and assessment of PCR for extraneous agent testing in IVMPs with examples from an Official Medicines Control Laboratory (OMCL).

Assessment of genetic, antigenic and pathotypic criteria for the characterization of IBDV strains.

The aim of this work was the selection and comparison of representative infectious bursal disease virus (IBDV) strains. Nine strains of IBDV, isolated at different times and from different geographic regions of Europe and China, were characterized. Batches of all strains were prepared following standardized protocols and checked for the absence of contaminating viruses. Criteria used for their characterization were: (i) the nucleotide sequence of the VP2 variable region, (ii) binding to a panel of neutralizing monoclonal antibodies in antigen capture enzyme-linked immunosorbent assays, and (iii) virulence in specific pathogen free chickens after infection with a standardized number of median embryo infective doses. Based on the first two criteria, two of nine strains were classified as classical virulent (cv) IBDV (F52/70, Cu-1wt), and five as very virulent (vv) IBDV (849VB, 96108, HK46, GX, Harbin). Remarkably, although a clear-cut difference was demonstrable between European cvIBDV (F52/70 and Cu-1wt) and vvIBDV (849VB and 96108) strains, there was a continuum in the pathogenicity of Chinese vvIBDVs. Our results indicate the probable existence of differences in virulence within IBDV lineages determined on the basis of antigenic typing using monoclonal antibodies and the alignment of the VP2 sequences. This indicates limitations in the analysis of IBDV pathotypes based on the VP2 variable region and emphasizes that these criteria may not be sufficient for the classification of IBDV strains.