ASK THE VET (Part I: Psittacine Beak and Feather Disease)

Psittacine Beak and Feather Disease (PBFD) is a devastating viral disease that, although first noticed in cockatoos, has been diagnosed in many species of birds. PBFD has been diagnosed in macaws, African Grey parrots, Eclectus, Rosellas, Lovebirds, budgies and cockatoos.

Neonates and young birds appear to be most susceptible to the virus. They possess a structure known as a cloacal bursa, or Bursa of Fabricius. This structure is unique to birds and is part of their immune system, the site of differentiation of immunologically competent B lymphocytes. This cloacal bursa is a common site of viral infection and lesion development. As a bird matures, the bursa undergoes regression and is almost gone by the time sexual maturity is reached. The clinical disease that develops depends upon the age of the bird and the stage of feather development. Young birds are most susceptible and are affected by an acute form of PBFD. This occurs during their first feather formation after replacement of down feathers. The developing feathers often fracture, bleed or fall out. Young birds may die following a short period of anorexia (loss of appetite),. depression and diarrhea, with very little feather abnormality.

Older birds are thought to develop a chronic form in which dystrophic feathers stop growing shortly after emerging from the follicles. The feathers become increasingly abnormal with each successive molt. Contour feathers are usually affected early, while primary feathers are affected later in the disease. Contour feathers often are lost over most of the body. New feathers may have retained feather sheaths, blood within the shafts, are curled and deformed, or are short and clubbed.

The beak may also be involved in the disease process. It may changed from a dull black to a glossy appearance. It may grow abnormally long and develop splits and cracks which break and peel. Bacteria and fungi often invade the abnormal beak, causing further destruction and necrosis (death) of the tissues. It often becomes difficult for the bird to eat because the beaks becomes very painful.

The disease is considered to be fatal. Some birds die shortly after showing signs of PBFD while others live months to years. Death usually occurs as a result of a secondary infection - bacterial, viral or fungal, since this disease attacks the immune system and makes the bird an "immunological cripple."

PBFD is spread by inhalation or ingestion of virus particles. Feather dust has been found to contain a large amount of virus. The virus has also been found in crop secretions and in fecal material. The virus may also be ingested as a result of preening.

The incubation period of variable among species and the age at which the bird is exposed. Again, neonates and young birds are felt to be most susceptible due to their possession of a cloacal bursa, while adult birds over two years of age are thought to be at less risk due to the involution of their bursas.

Next month: Part II, Diagnosis of PBFD