ASK THE VET (Part I: Avian Polyoma)
by Linda Pesek, DVM
Westbury Animal Hospital
319 Union Avenue
Westbury, NY
516-333-1123
This article first appeared in the April 1994 issue of SQUAWK, and appears here with their permission and the permission of the author.
All newly acquired birds, especially those to be used for breeding, should be screened for avian polyoma virus.
Avian polyoma virus causes high levels of mortality in young psittacine birds. It is thought that several strains of polyoma virus exist, with certain strains affecting one species and not others. Species differences in susceptibility to infection may also exist, since polyoma virus appears more prevalent in macaws, conures, Eclectus parrots, lovebirds, cockatiels and budgies than in other species.
Budgerigar Fledgling Disease (BFD) was the first identified acute generalized infection associated with avian polyoma virus. Clinical disease appears to depend upon the age and condition of the bird when exposed to the virus. In an infected flock, neonates can appear normal for the first ten to fifteen days and then die suddenly with full crops, while other hatchlings may develop swollen abdomens, discoloration of the skin, subcutaneous hemorrhages, head and neck tremors, ataxia and decreased down and contour feathers. Those infected budgies that survive may have symmetrical feather abnormalities such as dystrophic primary and tail feathers, and no down feathers on the back and abdomen. Primary and secondary feathers may fall out. These birds are often unable to fly. It is important to note that similar feather abnormalities may be seen with Psitticine Beak and Feather Disease (PBFD), but PBFD progresses, while feather abnormalities due to polyoma may resolve after several molts.
Larger psitticines may die suddenly without signs of illness, or die after showing depression, anorexia, weight loss, delayed crop emptying, regurgitating, diarrhea, dehydration, subcutaneous hemorrhages, dyspnea, ataxia and paralysis. Clinical signs are common at weaning and infected fledglings often die 12 - 48 hours after the development of clinical signs.
Both recovered budgies and larger psitticines are thought to remain infected, and serve as asymptomatic carriers.
A chronic form of polyoma virus is also thought to exist which causes weight loss, intermittent anorexia, polyuria, recurrent bacterial and fungal infections, and poor feathering.
Transmission:
Polyma 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.
Some asymptomatic adults produce persistently infected young, while others produce some normal neonates. Asymptomatic adults who intermittently shed virus are thought to be responsible for the persistence, transmission and spread of the virus.
Next month: Diagnosis, control and what to do with a positive bird.
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