Potentiating effects of manganese dioxide on experimental respiratory infections

Single and multiple 3-hour-long exposures to manganese dioxide (MnO₂) aerosol in respirable particle size, altered the resistance to bacterial and viral pneumonias. Increased mortality rates and reduced survival times were observed in mice exposed daily for 3 or 4 days to MnO₂ aerosol and challenged with airborne Klebsiella pneumoniae within 1 hour of termination of the last aerosol exposure. When the interval between the exposure and challenge was extended to 5 hours, the altered resistance to infection was seen already after a single 3-hour-long exposure to MnO₂ aerosol. Mice infected with airborne influenza virus 24 or 48 hours before initiation of the MnO₂ exposures also showed increased mortality rates, reduced survival times, and increased pulmonary lesions. The effect was more pronounced in mice exposed to MnO₂ at 48 hours after the infectious challenge.