Viruses Genomes - BEAK AND FEATHER DISEASE VIRUS

Beak and feather disease virus (Psittacine beak and feather disease) (PBFD) can affect all psittacine birds (Parrots, Cockatoos and Lorikeets) and possibly, Doves. The virus attacks the cells of the immune system and those which produce feather and beak. Affected birds gradually lose their feathers and develop beak abnormalities. Because the virus attacks the immune system, mortality occurs when affected birds succumb to infection by other diseases.

This disease was first described in Australian cockatoos in the early 1970's. Since that time, the disease has infected over 50 different species of birds. The virus causing the disease works slowly and is often referred to as "Bird AIDS". It is the most significant disease of psittacine birds in Australia.

PBFD has distinct features and in most circumstances a diagnosis can be achieved by veterinary examination alone. PBFD generally affects young psittacine birds, however, birds of all ages can succumb to the disease. Chronic PBFD is insidious in its development and progression; dystrophic feathers replace normal ones as they are moulted. A PBFD-affected bird can gradually lose its plumage without other signs of illness. The incubation period of PBFD can be as short as 21 days. Primary virus replication probably occurs in the bursa of Fabricius and/or gastrointestinal tract lymphoid tissue. Secondary virus replication occurs in the liver and thymus and probably other tissues. The target organ is the epidermis and the manifestation of skin disease requires a moult. Consequently, birds which become infected after feather development has completed may not develop clinical signs until their next moult. This could take six or more months. There is no treatment for the disease and it is usually fatal.
Susceptible birds can become infected through the oral cavity, nasal passages, and through the cloacae (the common receptacle in which the urinary, gastrointestinal and genital tracts empty). The virus is readily shed in the faeces and in the crop (storage part of the stomach). Viral particles in the crop may explain how the virus is passed from parents to offspring. High concentrations of the virus are shed in feather dust from infected birds.

PBFD is a circovirus, it measures 16 nm in diameter and the genome is a circular single-stranded DNA molecule. These characteristics make it the smallest known virus capable of causing disease.

References:

http://www.parrotsociety.org.au/articles/art_007.htm
http://numbat.murdoch.edu.au/caf/pbfd.htm
http://www.pethealthcare.net/html/body_psittacine_beak_and_feather_di.html
http://vetgate.ac.uk/browse/cabi/ae60c52bf022f2bb55f5a724216ca21c.html