ASK THE VET (Avian Polyoma Virus/Part II)
by Linda Pesek, DVM
Westbury Animal Hospital
319 Union Avenue
Westbury, NY
516-333-1123
This article first appeared in the May 1994 issue of SQUAWK, and appears here with their permission and the permission of the author.
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.
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