Persistence of Mastomys natalensis papillomavirus in multiple organs identifies novel targets for infection.

The high incidence of multiple wart formation and skin cancer in organ-transplant recipients, as well as the question of an involvement of papillomaviruses in a variety of human cancers, require a model system for papillomavirus infections in immunocompetent animals. Such an in vivo model is represented by the multimammate rat Mastomys coucha, which is infected with Mastomys natalensis papillomavirus (MnPV). MnPV primarily induces benign skin tumours, such as papillomas and keratoacanthomas. Here, the incidence of MnPV infections in different skin areas and various organs is described. In situ hybridization showed that hair follicle cells were positive for viral DNA and that the amount of MnPV in normal skin may be considered a predictor for the development of skin tumours. MnPV infection is not restricted to the skin, but can also be detected in inner organs. As the blood and the lymphatic system were temporarily also found to be virus-positive, a haematogenic propagation of MnPV can be assumed. However, MnPV is apparently not transmitted through the germ line, as fetuses and newborns lack viral DNA, despite infection of their mothers. In conclusion, M. coucha is not only useful to study papillomavirus-induced skin carcinogenesis, but may also serve as a model to identify additional, still unknown target cells of papillomavirus infections and the potential pathological impact.