Psittacine Beak and Feather Disease (PBFD) is a chronic disease characterized by feather dystrophy and loss, beak deformity and ultimately, death. The cause of PBFD is a newly discovered virus in the family Circoviridae. The disease probably originated in Australia and spread to other continents as a result of the shipment of birds for the pet bird trade. The disease has been reported in Australia, North America, Europe and Asia. Most species of parrots are susceptible to the virus however the species most commonly affected are cockatoos, African Grey Parrots, Eclectus Parrots and Lovebirds. The first clinically detectable sign of PBFD is the appearance of necrotic, abnormally formed feathers. Generally, PBFD is a disease of young birds (up to 3 years of age) however; it has been reported in birds over 20 years old that had been clinically normal most of their life. Peracute, acute and chronic disease patterns occur.
- Peracute– occurs in neonatal parrots. Clinical signs include diarrhea, lethargy, rapid weight loss and sudden death. Appears to be particularly common in young cockatoos and African Grey Parrots. Birds may die before any signs of abnormal feathers are seen. A correct diagnosis may be missed in birds that die from a peracute infection if a complete necropsy and thorough microscopic analysis of the tissues are not performed.
- Acute– occurs in young birds during the time of their first feather formation after the replacement of neonatal down. These infections are characterized by several days of depression followed by sudden changes in developing feathers including necrosis, fracture, bending, hemorrhage, or premature shedding of diseased feathers. The severity of feather changes depends on the number of feathers in a developmental stage at the time of infection.
- Chronic– occurs in birds that survive the acute phase of the disease. There is a progressive appearance of abnormal feathers during each molt. Signs include retention of feather sheaths, hemorrhage within the pulp cavity and fractures of the feather shaft. Short clubbed feathers, curled feathers, and circumferential constrictions of the feather shaft may also be present. If birds live long enough, they develop baldness as feather follicles become inactive. Certain species of birds may develop abnormally colored feathers. PBFD positive African Grey Parrots may show red body feathers in place of the normal gray feathers. Typically, beak deformities occur in birds following a protracted course of PBFD where substantial feather changes have occured. These changes include progressive elongation of the beak with necrosis of the palate area and transverse or longitudinal fractures of the beak. Usually, the upper beak is more affected than the lower beak.
The virus is spread from hen to the egg, hen to chicks being parent raised, and inhalation or ingestion of infected feather dust or feces. Viral particles in feather dust or dried feces can easily spread on clothing, nest materials, feeding formula or feeding utensils, nets, bird carriers, food dishes and air currents. The virus particles can remain viable in the environment for months, long after the infected bird is gone. Many birds infected with PBFD die with in 6-12 months of onset of clinical signs however, some birds have been known to survive 10-15 years. Death usually occurs from secondary bacterial, fungal, parasitic, chlamydial, or viral infections.
PBFD should be suspected in any bird that shows progressive feather loss and abnormal feather development. However one can not determine that a bird is infected with the virus just by examination of the feathers. Other disease processes can result in feathers with a similar appearance. Any factor that disrupts the blood supply to the developing feather, including trauma; bacterial or fungal infection of the feather follicles; other viral infections; malnutrition; hormone reactions; and some drug reactions, can cause feather changes similar to those seen with PBFD. Identical feather lesions to those caused by PBFD can be produced by pinching developing feathers at or near the level of the pulp cap. On the other hand, birds can carry the virus in their blood but have perfectly normal feathers. Until recently, the primary method of diagnosing PBFD was the demonstration of viral particles in the cells of the feather follicle and /or shaft. This required a surgical biopsy of the affected feather and it’s associated follicle. Since PBFD virus does not affect all feathers at the same time, this test could give a false negative result if the tissue sampled did not contain the virus. A more recent test, DNA probe analysis, tests for the presence of PBFD virus in the bird’s blood. This is the only effective method available for detecting the PBFD virus in a bird before feather lesions are present. The test requires a small amount of blood. Some birds may become infected with the virus, test positive, remain infected but never show clinical signs. Other birds, become infected, test positive, fight off the infection and subsequently test negative. Therefore, it is recommended to retest any PBFD positive bird 90 days after the initial test. If this bird tests positive a second time then it is infected however if subsequent test is negative, then the bird was able to eliminate the virus and is not infected. Since the virus survives in the environment, the DNA probe can also be used to test samples of feces and/or feather dust taken from the surfaces in the environment.
Management of a positive bird
If a bird from a breeding aviary tests positive for PBFD, remove the bird from the environment as quickly as possible. The bird can potentially shed large numbers of viral particles that can be spread to other birds by wind or on cloths, skin, hair or inanimate objects. All areas, supplies, and equipment should be cleaned, disinfected the tested with the DNA probe as mentioned above to determine if any infective material remains. In addition, I recommend testing of all birds exposed to the positive bird as well as any offspring of the infected bird.
If a companion bird tests positive then the bird should never be exposed to other birds outside of the household. Many infected birds can live a long life when provided a healthy, relatively stress free environment, good diet and regular veterinary care. Remember that you can carry the virus on your cloths.
To prevent spread of this disease, DNA probe testing is recommended on all cockatoos, lovebirds, Eclectus Parrots, African Grey Parrots and any birds showing feather lesions consistent with PBFD as part of a routine pre-purchase examination, prior to sale from an aviary or pet shop and prior to entry in to a new home/aviary. Research is ongoing for development of a vaccine against PBFD.
The primary information source for this article was the text book written by Dr. Branson Ritchie, Avian Viruses: Function and Control published in 1995 from Wingers Publishing Inc., Lake Worth, Florida. Branson Ritchie, DVM, PHD is an Associate Professor of Avian and Zoologic Medicine at The University of Georgia in Athens. He and his associates have been primarily responsible for the research into the cause of PBFD and for development of testing procedures for detection of this virus and are presently working on a vaccine for prevention of the disease.