Susceptibility of mouse mammary glands to murine gammaherpesvirus 72 (MHV-72) infection: evidence of MHV-72 transmission via breast milk

Murine gammaherpesvirus 72 (MHV-72) is a virus of wild rodents and serves a s a convenient small animal model to understand the pathogenesis of Epstein -Barv virus (EBV) and human herpesvirus 8 (HHV8) infection. In laboratory m ice MHV-72 causes an acute infection of lung epithelial cells and establish es the latency in B lymphocytes. In this study, we investigated athymic nud e and immunocompetent mice for distribution of virus in organs after infect ion with MHV-72. Ten days following subcutaneous dorsal injection of nude m ice, virus replicated in lungs, lymphoid organs, salivary glands and also i n mammary glands. The virus titre decreased by day 21 post-infection in for mer tissues, but increased in mammary glands. Presence of virus DNA sequenc es was detected in the lymphoid and non-lymphoid tissues until the death of the animals (about 1 month postinfection). Infection of immunocompetent mi ce with MHV-72 induced replication of virus up to 42 days post-infection in mammary glands reaching the highest level of infectious virus at day 8 pos tinfection. These data show that there is latent infection in mice never de tected before. Moreover, virus DNA was detected using nested PCR (by amplif ication of a portion of gp150 gene sequence) in the mammary glands and the milk of mouse mothers infected with MHV-72 2 days before delivery. We demon strated the presence of virus DNA also in the milk removed from the stomach of non-infected newborn mice, which were nourished by infected mothers (we t-nurses) for 1 or 2 days. The failure to detect the virus DNA in newborn m ice lungs confirmed that they did not become infected from wet-nurses by th e intranasal route. This suggests that MHV may be naturally transmitted to newborn mice via breast milk. (C) 2001 Academic Press.