Polyomaviridae
Polyomaviruses are DNA-based (double-stranded DNA, ~5000 base pairs, circular genome), small (40-50 nanometers in diameter), 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 (tumor-causing); 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 (poly-) tumors (-oma).
The family Polyomaviridae used to be one of two genera within the now obsolete family Papovaviridae (the other family being Papillomaviridae). 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 (JC virus), nephropathy (BK virus), and Merkel cell cancer (Merkel cell virus).
Until recently, the family of Polyomaviridae contained only one genus (Polyomavirus). The recent expansion of known Polyomaviruses called for reclassification of the family into 3 genera: Orthopolyomavirus, Wukipolyomavirus, and Avipolyomavirus.
Murine polyomavirus was the first polyomavirus discovered by Ludwik Gross in 1953. Subsequently, many polyomaviruses have been found to infect birds and mammals.
For nearly 40 years, only two polyomaviruses were known to infect humans. Genome sequencing technologies have recently discovered seven additional human polyomaviruses, including one causing most cases of Merkel cell carcinoma and another associated with transplant-associated dysplasia (TSV), that are natural infections of humans. Discovery of these polyomaviruses and other new—but previously undiscovered—viruses may provide clues to the etiologies for human diseases.
Polyomaviruses have been extensively studied as tumor viruses in humans and animals, leading to fundamental insights into carcinogenesis, DNA replication and protein processing. The tumor suppressor molecule p53 was discovered, for example, as a cellular protein bound by the major oncoprotein (cancer-causing protein) T antigen made by Simian vacuolating virus 40 (SV40). The avian polyomavirus sometimes referred to as the Budgerigar fledgling disease virus is a frequent cause of death among caged birds.
Read more about Polyomaviridae: History, Classification, Genome, Replication, The Polyoma Large and Small T-Antigen, The Polyoma Middle T-Antigen, Agnoprotein, Human Polyomaviruses, Diagnosis, Treatment