Avian polyomavirus (APV) was first discovered in budgies and was called Budgerigar Fledgling disease, although it has since been discovered that most species of psittacine birds are susceptible to infection.
It was found to be a nonenveloped, DNA virus and based on its size, shape, and DNA content it was classified as a papovavirus. The Papovaviridae contain two very different virus families, the papillomaviruses and the polyomaviruses. With further investigation, it was determined that the Budgerigar Fledgling Disease Virus is a polyomavirus.
Viral tranmisison can be both horizontal and vertical. This means birds can be infected from contaminated feather dust, faeces, urine, respiratory secretions and from parent to offspring.
APV targets nearly every system. Swollen bellies, skin bruising, tremors, wobbly, abnormal feathers may be seen. Larger psittacine species may live longer and show diarrhoea or regurgitation. Classical infections seem to affect larger species at around 7 weeks of age and can kill achieved a few hours of the first signs.
Adult birds are also affected. Signs resemble those of septicaemia and hepatitis.