Polyoma / Avian Polyoma

Index of Bird Diseases ... Symptoms and Potential Causes ... Bird Species and Diseases They are Most Susceptible to


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 bellies
    • Tremors
    • Weak, wobbly chicks
    • Abnormal feathers development
    • More 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.
Ernie Colaizzi  from The Research Associates Laboratoy (RAL) informed us that they employ a quantitative Real-Time PCR test to detect Polyomavirus.  All needed is a single drop of blood to detect infected and carrier states.  If blood is negative, the bird is not infected or a carrier.   Birds previously infected should be considered 'naturally vaccinated' and with a negative PCR for Polyomavirus not labeled a carrier.  Please refer to their website for information: vetdna.com ... We found these tests  to be quite affordable.  


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.

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


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