Polyomaviridae
Polyomaviruses are DNA-based, small, and icosahedral in shape, and do not have a lipoprotein envelope. Moreover, the genome possess early and late genes, contributing to its complex transcription program. They are potentially oncogenic; they often persist as latent infections in a host without causing disease, but may produce tumors in a host of a different species, or a host with an ineffective immune system. The name
polyoma refers to the viruses' ability to produce multiple tumors. The family
Polyomaviridae used to be one of two genera within the now obsolete family
Papovaviridae. The name
Papovaviridae derived from three abbreviations: Pa for
Papillomavirus, Po for
Polyomavirus, and Va for "vacuolating". Clinically, Polyomaviridæ are relevant as they contribute to pathologies such as Progressive multifocal leukoencephalopathy, nephropathy, and Merkel cell cancer. Until recently, the family of Polyomaviridae contained only one genus. The recent expansion of known Polyomaviruses called for reclassification of the family into 3 genera: Orthopolyomavirus, Wukipolyomavirus, and Avipolyomavirus.