Avian polyomavirus (APV)

Test code: S0089 - Qualitative detection of avian polyomavirus by polymerase chain reaction

S0089 is included in the psittacine PCR screening panel

Avian polyomavirus causes budgerigar fledgling disease. The virus has a double-stranded DNA genome. It has a worldwide distribution and is one of the most significant pathogens of fledglings of caged birds such as macaws, conures, eclectus parrots, ring-necked parrots, lovebirds, and budgerigars. Polyomavirus is highly infectious, although many infections may be asymptomatic. Disease in adult birds is rare and may require a simultaneous infection with Psittacine Beak and Feather Disease Virus.

Birds infected with APV can develop abdominal distention and a feather abnormality known as “French molt”. The disease causes a lack of down feathers on the back and abdomen, filoplumes on the head and neck, and subcutaneous hemorrhage, sometimes culminating in mortality. APV and PBFD (psittacine beak and feather disease) virus cause similar feather abnormalities and it is difficult to differentiate the viral etiology based on clinical presentations. However, it is important to differentiate them since treatments and countermeasures differ for the two diseases.

Viremia in budgerigars may develop as soon as 9 days after infection but may take as long as 2 weeks in other species. Following the start of viremia, virus can be detected in cloacal swabs. The sample of choice is blood as it has been shown in cockatoos and conures that viral DNA can be consistently detected in the blood of viremic birds but only intermittently in cloacal swabs. Infected nestling parrots can shed virus for up to 16 weeks, whereas adult birds may shed virus for only 6 weeks or less.

Many methods, such as immunoflourescence and electron microscopy, have been used to detect APV and differentiate APV infection from PBFD. Among these methods, PCR detection remains the most sensitive, specific and rapid (Phalen et al., 1991). Furthermore, a wide variety of samples can be tested using PCR, such as blood, cloacal swabs, fecal dust and fresh or paraffin-embedded tissue.

Some experts recommend screening individual birds without a history by PCR analysis of blood. Blood from adult birds testing positive for the virus should be retested in 4 to 6 weeks. Juvenile birds testing positive should be retested in 12 to 16 weeks. If the infected bird is blood-negative in the second test, an additional test should be done on a cloacal swab to ensure that it is no longer shedding virus in the droppings.

Preliminary trials indicate that polyomavirus DNA is not detectable in the blood of uninfected birds following vaccination for APV. Veterinarians must therefore conclude that if a bird’s blood tests positive by PCR, it is infected with polyomavirus regardless of whether it was recently vaccinated, and that the bird is most likely shedding the virus.

Utilities:

• Confirm the disease causing agent
• Environmental monitoring
• Ensure that bird populations are free of APV
• Early prevention of spread of the virus among bird populations
• Minimize human exposure to the virus
• Safety monitoring of biological products and vaccines that derive from birds

References:
Phalen, D.N., Wilson, V.G. and Graham, D.L. (1991) Polymerase chain reaction assay for avian polyomavirus. J Clin Microbiol.29:1030-1037.

Specimen requirements: 0.2 ml whole blood in EDTA (purple top) or ACD (yellow top) tube, or feces, or cloacal swab, or swab of the fresh outer surface of liver, spleen or kidney, or 0.2 ml fresh or paraffin-embedded tissue, shipped overnight at room temperature; or frozen tissue shipped frozen.

For specimen types other than those listed here, please call to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodology: Qualitative PCR

Normal range: Nondetected