Blue wing disease of chickens and viruses involved

Blue wing disease (BWD) is an acute disease in chickens that causes high mortality in 2-3 week-old chickens.The major pathological lesions are haemorrhages in skin and muscles especially on the wings, and gangrenous dermatitis and depletion of lymphocytes in lymphoid tissues; the thymuses being most severely damaged. There were, however, no specific lesions in the bone marrow in this study. Atrophy of bone marrow leading to severe anaemia is common in most other countries. BWD is also called chicken infectious anaemia (CIA) in these countries.The disease was suspected of being transmitted vertically from breeders to their progeny through the egg. BWD was not transmitted horizontally to other chickens kept in proximity.Chicken anaemia virus (CAV) and avian reovirus were isolated from diseased birds and it was possible to transmit the disease experimentally by parenteral inoculation with both CAV and reovirus. CAV alone did not cause any clinical signs of disease, but a cloned low pathogenic reovirus enhanced the pathogenicity of CAV, leading to clinical symptoms and increased mortality at 2 to 3 weeks after inoculation.A serological survey of antibody to CAV confirmed that CAV was transmitted from certain breeder flocks which were originally infected during egg production, demonstrated by a late seroconversion to CAV in these flocks.Prevalence of antibody to CAV in commercial broiler flocks at slaughter was relatively low. Sero-positive flocks were most often found in houses where outbreaks of BWD had occurred a short time before. Satisfactory sanitation of infected houses with standard cleaning and disinfection was difficult, but after 2-3 crops of chickens in these houses no antibody to CAV could be detected in the birds at slaughter