What is it?

Polyoma virus was initially reported in 1981 as the cause of Budgerigar Fledgling Disease, an often fatal disease in young Budgerigars (parakeets). Since then, it has been isolated from finches and nearly every species of parrots, as well as other species like chickens and pigeons. It is likely transmitted by ingestion or inhalation of feather dust, respiratory secretions, urates, or feces, though it is possible that it can be transmitted from the hen to the egg as well. Some birds, especially Budgerigars, can be persistently infected and shed the virus during stress, which may account for the increased incidence in flocks during the breeding season.

Clinical signs vary between species and age of exposure. In Budgerigars, disease generally occurs between 1 and 3 weeks of age, while other birds generally show clinical signs between 4 and 16 weeks of age. Older birds (over 1-5 months of age) exposed to the virus rarely develop disease, though a few cases have been reported primarily in immunocompromised individuals. Nestling birds often die suddenly without any clinical signs, though the breeder may notice abdominal distension and widespread bleeding. Infected individuals that survive generally exhibit feather abnormalities, depression, lack of appetite, weight loss, slow gastrointestinal motility, increased urination, neurological signs, or difficulty breathing.


A diagnosis begins with a complete medical history and a thorough physical examination. A veterinarian should perform a post-mortem examination on any bird that has died suddenly, especially if there are other birds in the environment. Swabs from the kidneys, liver, and spleen are generally diagnostic in these birds.

A serum chemistry panel and a complete blood count may show general signs of disease, but are not specific for polyoma virus. A polyoma polymerase chain reaction (PCR) test is available. This test detects the polyoma DNA. Generally, both blood and a swab of the oral cavity and cloaca are submitted. While this is a very accurate test, it can have false negatives in birds who are carriers. A positive test requires that the bird have either circulating virus in the bloodstream or are actively shedding virus in the droppings.


There is no specific treatment for birds infected with polyoma virus. Most young birds die prior to treatment. For older birds, several antiviral therapies have been tried and anecdotal evidence suggests that some are effective. Treatment is aimed primarily at supporting the immune system.


Prevention is the key with this disease, but recommendations will be different for the individual pet bird owner and the avian breeder. For those individuals who are planning to breed birds, consult with your veterinarian regarding specific recommendations for preventing disease in your aviary.

For the individual pet bird owner, this disease is of minimal concern, as most older pet birds have little risk of developing disease. If you are purchasing from a breeder, ask whether or not they are testing or vaccinating for polyoma and get a history of any previous outbreaks of polyoma in the past. It is best to purchase only birds that have already been weaned as older birds are less likely to have this disease.

If you are planning to bring a new bird into your house with other birds, you may consider screening for polyoma with the PCR test, though there are a number of other tests that are generally more important to perform in your new bird (such as Chlamydiophila, Pacheco’s (Herpes) Virus, and Psittacine Beak and Feather Disease Virus). Routine testing for this disease is becoming less common due to the relatively low risk of disease in older birds. However, if your new bird is a budgerigar or lovebird that will be entering a flock with other birds, especially young birds, testing should be done as these species are more likely to be asymptomatic carriers.

It is always important to practice good hygiene, especially if you will be going to bird nurseries, bird shows, pet stores, or other facilities that house a number of birds. Many of the infectious diseases that affect our birds can be brought into the household on clothing or our hands.

A vaccination for polyoma is available. It is an inactivated polyoma virus vaccine that can be administered after 5 weeks of age. The first injection must be repeated 2-3 weeks later, then annually for at-risk birds. There has been a great debate over the years regarding the polyoma vaccine. Most avian practitioners are not vaccinating for polyoma in pet birds. Because adult birds rarely develop disease even if infected with the virus, the risk of disease from polyoma is very low. If you are taking your bird to bird shows, bird clubs, or pet stores, there is a small risk and some owners still elect vaccination of their birds. Vaccine reactions are rare, though a local skin reaction can be seen occasionally.

In conclusion, polyoma virus causes disease primarily in nestling birds and rarely in adult birds. While both a PCR test and a vaccine are available, routine testing and vaccination is generally not recommended unless there is a specific risk to your bird.

Content prepared by St. Francis Animal and Bird Hospital, 1227 Larpenteur Ave. West, Roseville MN. 55113