Studies of culture conditions and environmental stability of human metapneumovirus

Human metapneumovirus (HMPV) is a paramyxovirus that is a leading cause of acute respiratory disease. HMPV is difficult to cultivate and limited published data describe the in vitro growth characteristics of the virus and its ability to replicate in different cell lines. Stability of HMPV to different temperatures or environmental conditions has not been described. Nosocomial infections due to HMPV have been reported, and thus the survival of infectious particles on environmental surfaces is important. We tested multiple cell lines for the ability to support HMPV replication both in the presence and absence of exogenous trypsin. The most permissive monkey kidney epithelial cells were LLC-MK2 and Vero, while the most permissive human airway epithelial cell line was BEAS-2B. LLC-MK2 cells were tolerant of trypsin and thus remain an ideal cell line for HMPV cultivation. Spinoculation significantly increased the infectivity of HMPV for cells in monolayer culture. Infectious virus was very stable to repeat freeze–thaw cycles, ambient room temperature, or 4 °C, while incubation at 37 °C led to degradation of virus titer. Finally, nonporous materials such as metal or plastic retained infectious virus for prolonged periods, while virus deposited on tissue and fabric rapidly lost infectivity. These findings provide guidance for laboratories attempting to culture HMPV and relevant information for infection control policies.