Polyomavirus in Non-budgerigar Psittacine Birds - Page 2

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Polyomavirus in Non-budgerigar Psittacine Birds

By: Dr. Branson Ritchie

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Testing in Live Birds

Until the avian polyomavirus vaccine was registered by the USDA, control of polyomavirus outbreaks was problematic because of the commonality of virus activity in psittacine birds and the inherent difficulties in reducing potential exposure to this environmentally stable virus by maintaining closed aviaries, practicing extraordinary hygiene and attempting to detect and isolate transiently-infected birds.

Techniques originally developed at the University of Georgia College of Veterinary Medicine to facilitate this latter task include assays to detect anti-polyomavirus antibodies and a DNA probe test to detect polyomavirus nucleic acid. An antibody assay can be used to determine if a bird has been previously infected with the virus (the speed of decay of detectable levels of antibodies varies with the individual bird).

A lack of an antibody titer may indicate either that the bird has not been infected, that it was infected in the distant past and the antibody titer has decreased below a detectable level, or that it has been infected but has not developed an antibody response (considered rare with avian polyomavirus). Polyomavirus nucleic acid can be detected in cloacal swabs (fecal samples) taken from psittacine birds during an outbreak. This allows birds that are excreting nucleic acid to be isolated from the remainder of the flock until the infection has resolved in the positive birds. Polyomavirus-specific DNA probes also can be used to detect viral nucleic acid in environmental samples collected from a bird's living area (home, nursery, incubators, etc.) that may have been contaminated with the virus.

If one chooses to use any diagnostic test for polyomavirus, it is important to ask what question is to be answered. If the question is whether a bird has been previously infected with polyomavirus, then the test that is most likely to provide this information is an antibody assay. Antibody titers will persist long past the time that a bird has cleared an infection.

If the question is whether a bird represents an immediate threat to other birds in a group, then the best test to run is a DNA probe assay on excrement. If testing is chosen for attempted control of polyomavirus in lieu of vaccination, then using both a test to demonstrate if polyomaviral nucleic acid can be detected in excrement, or blood, and a test to demonstrate if virus-neutralizing antibodies are present is recommended.

Confirming an Infection

Neonates that die from avian polyomavirus are usually in excellent overall condition and may have full crops and alimentary tracts, indicating a rapid illness and death. Typical abnormalities noted at necropsy include enlargement of the liver and spleen and hemorrhage under the skin and on the surface of many internal organs.

The most accurate way to confirm the presence of avian polyomavirus infection is the recovery of the virus in cell culture; however, this procedure is time-consuming and expensive. Other techniques that can be used to document an active polyomavirus infection include: the demonstration by electron microscopy of virus particles in affected tissues; demonstration of a four-fold increase in antibody titer in paired samples run at the same time in the same laboratory; specialized staining of suspect lesions using viral-specific antibodies; or the detection of viral nucleic acid in affected cells using polyomavirus-specific DNA probes.

To find an avian veterinarian in your area that can test for polyomavirus contact the Infectious Disease Laboratory at the University of Georgia College of Veterinary Medicine (706-542-8092).

Controlling an Outbreak

Steps to controlling a polyomavirus outbreak should include isolating clinically affected birds and any birds to which they have been exposed, vaccinating the adults and neonates to stimulate flock immunity and cleaning and disinfecting the contaminated facility.

While vaccinating during a polyomavirus outbreak has been shown to be advantageous, it should be stressed that deaths may continue in neonates until flock immunity has been increased, generally 2 to 3 weeks after the last booster vaccination.

Great care should be exercised when handling birds during an outbreak to make certain that aviary personel do not disseminate the virus.

  • The nursery or housing area should be thoroughly cleaned and disinfected to prevent virus contaminating this environment from infecting neonates before the time that their immune systems will respond to vaccination.

  • Contaminated nest boxes must be replaced. A DNA probe-based assay is valuable for identifying birds that are shedding viral nucleic acid in their excrement during an outbreak. Birds that are shedding viral nucleic acid should be separated from others to reduce potential virus transmission, while vaccinated birds are developing immunity to the virus.

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