Influenza enhances susceptibility to natural acquisition of and disease due to Streptococcus pneumoniae in ferrets.

The role of respiratory viruses in the transmission of Streptococcus pneumoniae is poorly understood. Key questions, such as which serotypes are most fit for transmission and disease and whether influenza virus alters these parameters in a serotype-specific manner, have not been adequately studied. In a novel model of transmission in ferrets, we demonstrated that pneumococcal transmission and disease were enhanced if donors had previously been infected with influenza virus. Bacterial titers in nasal wash, the incidence of mucosal and invasive disease, and the percentage of contacts that were infected all increased. In contact ferrets, viral infection increased their susceptibility to S. pneumoniae acquisition both in terms of the percentage infected and the distance over which they could acquire infection. These influenza-mediated effects on colonization, transmission, and disease were dependent on the pneumococcal strain. Overall, these data argue that the relationship between respiratory viral infections, acquisition of pneumococci, and development of disease in humans needs further study to be better understood.