It was originally described in 1967 by Arnold Graffi as a cause of epithelioma in Syrian hamsters (Mesocricetus auratus).

At around 5.3 kilobase pairs in length, it contains genes for the small, middle, and large tumor antigens and three viral coat proteins, VP1, VP2, and VP3.

[2] HaPyV and MPyV are closely genetically related; until recently, they were the only two members of the polyomavirus family known to express the middle tumor antigen protein, 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.

[8] Following the typical pattern for polyomaviruses, the HaPyV viral capsid contains three proteins: VP1, VP2, and VP3, of which VP1 is the primary component.

However, the HaPyV capsid differs from its close relative MPyV and from another well-studied polyomavirus, SV40, in having a T=7 levo rather than dextro symmetry.