Economically important non-oncogenic immunosuppressive viral diseases of chicken--current status.

Immunosuppressive viral diseases threaten the poultry industry by causing heavy mortality and economic loss of production, often as a result of the chickens' increased susceptibility to secondary infections and sub-optimal response to vaccinations. This paper aimed to present an up-to-date review of three specific economically important non-oncogenic immunosuppressive viral diseases of chickens, viz. chicken infectious anaemia (CIA), infectious bursal disease (IBD) and hydropericardium syndrome (HPS), with emphasis on their immunosuppressive effects. CIA and IBD causes immunosuppression in chickens and the socio-economic significance of these diseases is considerable worldwide. CIA occurs following transovarian transmission of chicken anaemia virus and has potential for inducing immunosuppression alone or in combination with other infectious agents, and is characterized by generalized lymphoid atrophy, increased mortality and severe anemia. The virus replicates in erythroid and lymphoid progenitor cells, causing inapparent, sub-clinical infections that lead to depletion of these cells with consequent immunosuppressive effects. The IBD virus replicates extensively in IgM(+) cells of the bursa and chickens may die during the acute phase of the disease, although IBD virus-induced mortality is highly variable and depends, among other factors, upon the virulence of the virus strain. The sub-clinical form is more common than clinical IBD because of regular vaccination on breeding farms. Infection at an early age significantly compromises the humoral and local immune responses of chickens because of the direct effect of B cells or their precursors. HPS is a recently emerged immunosuppressive disease of 3-6-weeked broilers, characterized by sudden onset, high mortality, typical hydropericardium and enlarged mottled and friable livers, with intranuclear inclusion bodies in the hepatocytes. The agent, fowl adenovirus-4, causes immunosuppression by damaging lymphoid tissues; the presence of IBD and CIA viruses may predispose for HPS or HPS may predispose for other viral infections. Synergism with CIA or other virus infections or prior immunosuppression is necessary to produce IBH-HPS in chickens and the susceptibility of chickens infected with fowl adenovirus varies throughout the course of CIA infection. The mechanism of immunosuppression has been studied in detail for certain chicken viruses at molecular levels, which will provides new opportunities to control these diseases by vaccination.

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).