Avian Polyoma Virus

Original print -- American Cockatiel Society magazine.
Most bird owners are unaware of the devastating impact this viral infection can have or the simple precautions that can be taken to prevent an outbreak. The birds that we need to worry about most with this disease are the young Psittacines between 2 weeks and 5 months of age. Birds that are infected during this time will die, most commonly at weaning. If infected later they will not show any signs, but may become carriers. Carriers are dangerous because they don't look sick, are difficult to test for unless they are shedding the virus at the time, but may shed the virus when there are babies around and hence kill them. A bird infected with Polyoma virus can show no symptoms, appear completely healthy in all respects and may not shed the virus until placed in a situation involving stress. (Such stresses may include bleeding, undersized cages, being placed in too close proximity to birds of different species, etc.)

What is Avian Polyoma Virus?
Avian Polyoma Virus (APV) was first discovered in 1981 in budgies and was called Budgerigar Fledgling disease. It is a virus in the Polyoma family, a group of very small unencapsulated viruses. (Viruses are small infectious proteins, which need living cells to reproduce.)

What Species does it attack?
Fortunately, Polyoma Virus does not effect humans, however, it is devastating to bird populations and appears to threaten a wide variety of birds including: Macaws, Amazons, Conures, White Billed Caiques, Parrotlets, African Greys, Lovebirds, Ring Necked Parakeets, Eclectus, Scarlet Chested Parrots', Bourke's, Cockatoos, Cockatiels, Budgerigars and Finches.

Polyoma virus is thought to spread both horizontally (bird to bird) and vertically (via the 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.

What does it do and what are the symptoms?
APV targets just about every system, and can be seen in many of the organ systems. As the vital organs fail, the body is unable to process food, crop stasis occurs and the bird dies from dehydration even though the crop is full Sometimes subcutaneous hemorrhaging (bleeding under the skin) occurs and other infections may have set in. Adults may experience weight loss, recurrent bacterial and fungi infections and poor feather formation. They may appear to recover, but die months later from renal failure. If birds infected with APV are bred, nesting and laying can appear normal Chicks sometimes die in the shell or hatch in a very weak state, only to die within hours. Other chicks may hatch just fine and appear to be thriving for as long as 15 days, however, due to weakening of the vital organs and the immune system, the body cannot support its own growth and the chicks die acutely, within hours with full crops. As the vital organs fail, the body is unable to process food, crop stasis occurs and the chick dies of dehydration although the crop is full Some chicks live longer, but fail to thrive. They may have poor muscle tone, swollen abdomens, be unable to fly and never learn to feed themselves. Still others may seem completely normal, other than being slow to row and feather out. These chicks learn to fly and eat on their own and appear completely normal, but they may be carriers of the virus and go on to infect others and their offspring.

How do birds get APV?
Affected birds may shed the virus intermittently. Parents may infect offspring through vertical transmission into the egg before laying, regurgitation of food, via exfoliated crop cells. Fostered eggs and chicks can pass the virus on to new parents. The virus can be shed in feather dust and transmitted through breathing the air near an infected pair. Studies suggest that the virus could be shed from all bodily functions, reproductive, gastrointestinal and renal functions, so the virus may appear in feces, urine, eggs and sperm. The virus may also be exhaled and in turn inhaled by others. People who care for birds may inadvertently transmit the virus through their own breathing actions, as well as by contact with the dust on clothing and debris on shoes.

What is the cure?
There is no known cure, but a vaccine is available, not readily, in Canada, and it can be costly. Baby birds can be vaccinated at 5 weeks of age with a booster 2 to 3 weeks later. If there is an outbreak in your aviary, all birds should be vaccinated annually to help them protect against the virus and to decrease the concentration of the virus in the environment.

What can we do to prevent it?
For the health of the rest of the flock, all new birds, no matter what the source, should be quarantined and vet checked before introduction to your own collection. There are several schools of thought as to how long the quarantine should last. Recommendations range from 30 to 90 days. Ask your vet and follow his/her recommendation. Nursery management is a very important factor, how babies are fed, using the same tools for hand feeding instead of fresh ones for each clutch, not mixing species together, keeping species separate. When you are visiting another aviary, follow a set of rules. Change clothes before and after the visit, so that you do not inadvertently bring something in on your clothing or shoes. Do not handle the birds unless you are invited to and disinfect your hands before and after. The source of an infection of APV into an aviary is almost impossible to identify. Birds taken on visits or to public displays can contract the virus simply by being close to an infected bird, or it's care giver. Virus particles can also he passed on in dust on books or other aviary equipment moved from an infected aviary to an uninfected one. It can be spread from second-hand cages, nest boxes, used seed cups, etc., which are not thoroughly cleaned and disinfected before coming into a home or aviary with birds. A.V. can rapidly spread once established in an aviary. Particles can evaporate into the air from feces as they dry, can spread through airflow, disturbance of even the smallest amount of dust and physical contact of care givers. A.V. particles aver very resistant in the environment. They can survive in extreme heat and can contaminate an environment for an extended period of time. There is no information as to just how long. Polyoma is also very resistant to many disinfectants, however, chlorine bleach is thought to be effective, as well as sodium hypochlorite. Any chicks that die in the nest for no apparent reason should be taken, within 24 hours or sooner, to an avian pathologist for necropsy. Fresh samples are necessary to identify the virus. Live birds can be tested for A.V. By an avian veterinarian, however, the testing is not cheap, as samples must be sent to the U.S.A. for analysis. The best defense is prevention. Education about this infection is the first line of defense in protecting our feathered friends.

In closing, Polyoma is out there, yes, it can have devastating effects but it can also be managed. We can all start by examining our own practices and following the hygiene guidelines, so many people believe are only for those "big bird owners". We can cut down thc incidence of this virus by how we manage our own aviaries.

Species differences in susceptibility to polyoma virus are thought to exist. Macaws, conures, Eclectus, African greys and Amazons are thought to be very susceptible to infection. Polyoma virus can be present in a carrier state, with adult birds appearing clinically normal until they undergo stress. One type of stress that can cause a latently infected bird to shed virus is breeding. Increases in reproductive hormones -- estrogen, progesterone, and testosterone -- are thought to have an effect on the immune system and may be responsible for the activation, multiplication and shedding of the virus.

Detection of polyoma 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.

Since polyoma is a very infectious virus causing high mortality and morbidity in young birds, closed breeding aviaries are recommended. A cloacal swab should be checked on all birds leaving an aviary and all newly acquired birds before being introduced into a collection. Once the virus is introduced into a collection it is almost impossible to eliminate. This is because of carrier states that exist and because the virus is very resistant to many disinfectants. Because a high incidence of polyoma exists in budgies and cockatiels, it is recommended by some that these birds not be kept on the same premises where other species are housed and bred. Work is currently being done to try to produce a vaccination to protect against polyoma. Although results look promising, no vaccination is yet available. A bird positive for polyoma may be kept as a pet as long as it is in a single bird household. It should never come in contact with neonates (young birds) or birds to be used for breeding.

Possible Vaccination
Polyoma virus is a very stable virus in the environment, much like Parvo virus in dogs we expect it can live six months in the environment. It is easy to transmit by dust from pet shops, other bird owners homes or bird shows and fairs. Most birds acutely infected with Polyoma virus die within a few days and no specific treatment for the virus is available. Most birds that die from Polyoma are under 100 days of age, BUT IT CAN AFFECT ANY AGE BIRD. Polyoma virus is VERY COMMON across America, and there have been outbreaks from local and distant shows in some areas for the last six years.


E-Mail: berniehansen@sympatico.ca



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Hamilton & District Budgerigar Society Inc.