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.
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. 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.