Chicken anaemia virus infection (known generally in the industry as CAV) is an acute viral infection of chickens that is found worldwide. The disease is not known to affect any other bird species, although antibodies have been found in Japanese (coturnix) quail. Prior to confirmation that the disease was in fact caused by a virus, it was known as Chicken Anaemia Agent or CAA.
CAV can infect chickens of all ages but the disease is only seen in young chickens and is characterised by depression, anaemia, inappetence, haemorrhage and a sudden rise in mortality. CAV depresses the immune system and therefore leaves affected birds more susceptible to other infections and mortality can often be a result of secondary infections.
CAV is a small DNA virus. In healthy chicks, susceptibility to disease declines rapidly with age and chicks are resistant to the clinical signs of the disease at 2 weeks of age. The virus can be spread both vertically (from parents to offspring) and horizontally (between birds within a flock), via the faecal-oral route.
Infected birds are viremic (shed virus) for up to 35 days. Infected roosters will shed the virus in their semen and hens will shed the virus into eggs during this viremic period. Chicks infected through their parents can spread the virus to other susceptible chicks with which they have contact, either directly or indirectly.
Recovered or immunised birds have neutralising antibodies that protect them from further infection. Chicks from immune breeder hens will be protected by maternal antibody until their own age resistance develops. Protection by maternal antibodies can, however, be overcome if the chick is affected by another severe immunosuppressive disease, such as infectious bursal disease, Marek’s disease or reticuloendotheliosis.
There is no specific treatment. Secondary bacterial infections may be treated with antibiotics and minimised through good biosecurity practices, including hygiene and management. Vaccination of antibody-negative breeder flocks prior to the start of egg production is recommended. The control of other diseases that suppress the immune system is also important. At present, there is no vaccine available to prevent subclinical losses in broilers.