Hamster polyomavirus

Hamster polyomavirus (abbreviated HaPyV or HaPV) is an unenveloped double-stranded DNA virus of the polyomavirus family whose natural host is the hamster. It was originally described in 1967 by Arnold Graffi as a cause of epithelioma in Syrian hamsters. Among the polyomaviruses, its closest relative is mouse polyomavirus (MPyV), with which it shares many genetic features. Until recently, hamster and mouse polyomaviruses were the only two members of the family known to express a protein called middle tumor antigen, which is uniquely efficient at inducing neoplastic transformation in infected cells, resulting in transformation in in vitro cell culture and in the formation of tumors in vivo. In 2015 the genome sequence of a rat polyomavirus was reported to contain middle tumor antigen as well, consistent with expectations that it evolved uniquely in the rodent lineage of the polyomavirus family.