LanguageChicken Infectious Anaemia Virus (CAV) can be isolated in all countries with intensive poultry production. It damages the thymus of very young chickens and at the same time negatively affects the development of blood cells and the immune system. As a result the amount of red blood cells and T-lymphocytes is reduced in infected chickens.
Clinically infected birds may appear pale, depressed and show reduced weight gain. In pathological examinations anaemia, haemorrhages, atrophy of the thymus and changes in the bone marrow can be found.
Furthermore the reduction of T-lymphocytes leads to immune-suppression, reduced production of antibodies and higher susceptibility to secondary infections.
Besides the clinical form of CAV (mostly seen in birds without maternal antibodies against CAV), also sub-clinical CAV has to be considered when it comes to economic losses caused by the disease. Broilers that have very low maternal antibody levels at hatch, become infected with CAV at a relatively early age. They may appear healthy, but show CAV titers around day of slaughter. Analysis of production parameters of such flocks shows that feed conversion and weight gain are lower compared to birds negative for CAV titers at slaughter.
The disease normally occurs when layer or broiler breeder flocks with no previous exposure to the virus become infected during production. Under these conditions, the virus is transmitted via the hatching egg (vertically) to the progeny, which show clinical signs of the disease from 10-14 days of age. CAV can also spread horizontally in a contaminated environment to the progeny of breeders which are not protected by maternal antibodies.
In order to protect young birds from getting infected and to improve performance of broilers, vaccination of breeder flocks with live vaccines is the method of choice. By vaccinating young breeder pullets between 12-15 weeks of life, they have enough time to develop high levels of antibodies against CAV before being transferred to the laying house. When egg production starts, they will transmit those antibodies to their progeny and by that protect them against early infections with CAV. Besides that, vaccination also stops the horizontal spread of virus from possibly infected breeders, which again lowers the risk of susceptible birds to become infected by direct or indirect contact.
