Polyomaviruses of birds:: Etiologic agents of inflammatory diseases in a tumor virus family

Since their first detection in 1981 (7, 9), the polyomaviruses of birds have been known to cause acute and chronic diseases in several species of birds. Polyomavirus disease of parrots caused by avian polyomavirus (APV) (50, 70) and hemorrhagic nephritis and enteritis of geese (HNEG) caused by goose hemorrhagic polyomavirus (GHPV) (27, 57) are inflammatory diseases characterized by high mortality rates in young birds. The high pathogenicity of polyomaviruses of birds is in contrast to the innocuous persistent infections that the intensively studied mammalian polyomaviruses, such as simian virus 40 (SV40), usually cause in their natural nonimmunocompromised hosts (30, 48). The mammalian polyomaviruses are well known to induce tumors after inoculation into nonpermissive laboratory rodents (4, 14, 23); such events have never been observed for birds with APV or other bird polyomaviruses. Here, we review the available literature on polyomaviruses of birds, focusing on the characterization of the known viruses and the diseases caused by them and on approaches to investigate the mechanisms for their pathogenicity.