The novel human polyomaviruses HPyV6, 7, 9 and beyond

Since the discovery of Merkel cell polyomavirus and its causative association with Merkel cell carcinoma (MCC), six human polyomaviruses (HPyVs) have been identified that, so far, lack any disease association, which include the human polyomaviruses (HPyV) 6, 7, 9, 10 and 12 as well as the Saint Louis polyomavirus (STLPyV). PCR studies revealed that HPyV6 and HPyV7 are shed from the skin of healthy subjects and of patients suffering from various skin tumours. HPyV6, 7 and 9 were sporadically detected in body fluids and excretions of immunocompromised patients and healthy subjects. HPyV10 was identified in papillomavirus-induced anal condylomas, and variants of HPyV10, named MWPyV and MX polyomavirus (human) (MXPyV), as well as STLPyV were detected in faeces of diarrheal and healthy children. HPyV12 was discovered in organs of the digestive tract of patients suffering from various malignant diseases. Serological studies using capsomer-based or virus-like particle (VLP)-based enzyme-linked immunosorbent assay (ELISA) revealed that HPyV6, 7, 9 and 12 are circulating in the human population. As all other HPyVs, the novel polyomaviruses encode small and large T antigens and thus are potentially oncogenic. However, several studies have revealed a lack of association of HPyV6, 7 and 9 with numerous human tumours. In the future, it will be important to unravel the cell types and body compartments of the novel HPyVs reservoir and to search for possible associations with cancer and non-malignant diseases.