Chicken anaemia virus

Chicken anaemia virus, or CAV, is currently a member of the anelloviridae family which is found worldwide. The virus only affects chickens. CAV is a non-enveloped icosahedral single stranded DNA virus, which causes bone marrow atrophy, anaemia, and severe immunosuppression. Clinical signs of CAV infection are predominantly found in young chicks due to vertical transmission from the breeder hens whose maternal antibodies have not yet formed following exposure. Clinical disease is rare today because of the widespread practice of vaccinating breeders, but the subclinical form of the disease—which normally affects birds more than two weeks of age following horizontal transmission of the virus via the oro-faecal route—is ubiquitous. The virus is very resistant in the environment, making elimination very difficult. The disease/virus has many names including chicken anaemia, blue wing disease, anaemia dermatitis syndrome, chicken/avian infectious anaemia, haemorrhagic aplastic anaemia syndrome, infectious chicken anaemia, chicken infectious anaemia virus and chicken anaemia agent. When this virus was first discovered in 1979, it was named chicken anemia agent. Clinical signs only occur in chicks less than three weeks of age. During outbreaks of CAV, up to 10% of chicks can die. Signs include a pale comb, wattle, eyelids, legs and carcass, anorexia, weakness, stunting, unthriftiness, weight loss, cyanosis, petechiation and ecchymoses, lethargy and sudden death. Neurological signs include dullness, depression and paresis. In older chickens, subclinical infection (an infection with no apparent signs) may cause reduced growth rates due to a poor feed conversion rate. Chicken anaemia virus infects preursor T cells in the thymus and hematopoietic stem cells in the bone marrow, causing destruction of these cells via apoptosis.This reduces the production of red blood cells (RBC) and white blood cells (WBC), leading to severe immunosuppression and anemia. A presumptive diagnosis can be made based on the clinical signs and a low haematocrit reading (<27%). Virus isolation, increased antibody titres, immunoperoxidase staining, ELISA, PCR or indirect immunofluorescence can be used to confirm the presence of the virus. Post mortem finding show significant atrophy of the lymphoid organs, haemorrhage throughout the tissues and pale watery bone marrow. There is no specific treatment for infected birds. Culling of infected birds is normally performed in infected commercial flocks. Birds that have been infected develop immunity to the virus. Vertical spread of the disease can be controlled by the vaccination of breeding hens with both live attenuated and wild vaccines. These vaccines reduce the vertical transmission rate. The vaccine has the ATCvet code QI01AD04 (WHO). Appropriate hygiene and biosecurity measures may be employed to control the disease.