Polyoma / Avian Polyoma

The Avian polyoma virus (also known as Budgerigar Fledgling Disease) causes high levels of mortality in young psittacine birds. Polyoma is transmitted primarily bird to bird but it is also thought to be transmitted via the egg.

Polyoma virus appears to be most prevalent in:

Avian Polyoma is most commonly recognized in chicks:

  • Classical infections seem to affect larger species at around 7 weeks on age and can kill within a few hours of the first signs with chicks showing large bruise-like haemorrhages under the skin
  • Other common symptoms:
    • Swollen belliesTremorsWeak, wobbly chicksAbnormal feathers developmentMore detailed information on disease progression below …

Larger psittacine / parrot species may live longer and show the following symptoms:

  • Signs resemble those of blood poisonings (epticaemia) and liver disease (hepatitis).
  • Typical symptoms are:
    • Diarrhea
    • Regurgitation

Embryonic death or decreased hatchability can also be caused by Polyomavirus.

  • More detailed information on disease progression below …

Symptoms / Progression:

Neonates with polyomavirus infections may bleed profusely, or for a prolonged period, from intramuscular injection sites or from follicles where feathers have been removed. Subcutaneous hemorrhage over the crop and across the skull is common.

Those exposed to this virus at two to four weeks of age may develop feather abnormalities.

Disease symptoms: anorexia (appetite loss), depression, delayed crop emptying, and subcutaneous hemorrhages. Older psittacines that are exposed to polyoma virus may develop subclinical infections but remain infected.

Budgerigar Fledgling Disease (BFD) was the first identified acute generalized infection associated with avian polyoma virus. In an infected flock, neonates can appear normal for the first ten to fifteen days and then die suddenly with full crops, while other hatchlings may develop swollen abdomens, discoloration of the skin, subcutaneous hemorrhages, head and neck tremors, ataxia and decreased down and contour feathers.

Those infected budgies that survive may have symmetrical feather abnormalities such as dystrophic primary and tail feathers, and no down feathers on the back and abdomen. Primary and secondary feathers may fall out.

These birds are often unable to fly. It is important to note that similar feather abnormalities may be seen with Psittacine Beak and Feather Disease (PBFD), but PBFD progresses, while feather abnormalities due to polyoma may resolve after several molts.

Larger psittacines may die suddenly without signs of illness, or die after showing depression, anorexia, weight loss, delayed crop emptying, regurgitating, diarrhea, dehydration, subcutaneous hemorrhages, ataxia and paralysis. Clinical signs are common at weaning and infected fledglings often die 12 – 48 hours after the development of clinical signs.

All newly acquired birds, especially those to be used for breeding, should be screened for avian polyoma virus.

A chronic form of polyoma virus is also thought to exist which causes weight loss, intermittent anorexia, polyuria, recurrent bacterial and fungal infections, and poor feathering.

Recovered psittacines are thought to remain infected, and serve as asymptomatic carriers.


Many birds are subclinically infected and shed the virus in respiratory secretions, crop secretions, feather dust and droppings during times of stress such as during the breeding season.

The Polyma virus is thought to spread both from bird to bird and from bird to egg. Parents may transmit the virus to their offspring when feeding by regurgitation of exfoliated crop epithelial cells. The virus can replicate in feather follicles and thus be shed in feather dust (like PBFD).

The virus may also be shed in the urine. Susceptible hosts may be infected by inhalation or oral ingestion. Although young birds are most susceptible, adult birds may also develop disease.

The exact incubation period is unknown but may be anywhere from 1 to 2 weeks. Affected budgie fledglings show peak mortality rates between 15 – 19 days of life, while larger parrots may show signs between 20 – 56 days of age.

Some asymptomatic adults produce persistently infected young, while others produce some normal neonates. Asymptomatic adults who intermittently shed virus are thought to be responsible for the persistence, transmission and spread of the virus.


Postmortem detection of polyoma is based upon finding viral intranuclear inclusion bodies in the liver, kidney, spleen, heart and feather follicles.

Identification of the virus in a live bird can be very difficult. Early tests looked for the presence of antibodies or proteins produced by the body against the virus. These antibodies, however, may no longer be present in a bird that remains infected by the virus.

No correlation exists between serum neutralizing antibodies and viral shedding. This means that a bird could have a negative antibody titer and still shed the virus, or a positive antibody titer and not shed virus.

A new test, a DNA PCR probe test has been developed by Avian Research Associates. This test is able to detect polyoma virus in live birds that are shedding virus by analyzing cloacal swabs. The limitation of this test, however, is that a cloacal swab identifies only a bird who is shedding the virus at the time of sampling. A latently infected bird may not be shedding virus.

Thus, a positive test indicates viral nucleic acid was found in the sample and confirms viral shedding, while a negative test indicates that the individual was not shedding virus at the time the sample was taken. It does not necessarily indicate the bird is free of the virus.

Possible sample material:

  • 1-2 freshly plucked feathers from the birds chest or tail (no discarded feathers or downs)
  • 1-2 drops of EDTA whole blood.
  • Post mortem material or cloacal swab

There is a comprehensive testing package offered by Avian Biotech


A vaccination for polyoma is available. Neonates may be vaccinated at 40 days of age and boosted two weeks later. They are considered protected two weeks past their second vaccination.

Yearly boosters are recommended. Breeding birds should be vaccinated twice several months before breeding season.

Find Your Local Avian Veterinarian

Information contained on this website is provided as general reference only. For application to specific circumstances, professional advice should be sought.

Photo of author

Team Beauty of Birds

Beautyofbirds.com's team of experts includes veterinarians, biologists, environmentalists and active bird watchers. All put together, we have over half a century of experience in the birding space.

You can meet our team here.
Team Beauty of Birds is separate from the “Parrot Parent University” parrot training course and its instructors.