High temperature (30 degrees C) blocks aerosol but not contact transmission of influenza virus

Abstract

Influenza causes significant morbidity in tropical regions; however, unlike in temperate zones, influenza in the tropics is not strongly associated with a given season. We have recently shown that influenza virus transmission in the guinea pig model is most efficient under cold, dry conditions, which are rare in the tropics. Herein, we report the lack of aerosol transmission at 30 degrees C and at all humidities tested. Conversely, transmission via the contact route was equally efficient at 30 degrees C and 20 degrees C. Our data imply that contact or short-range spread predominates in the tropics and offer an explanation for the lack of a well-defined, recurrent influenza season affecting tropical and subtropical regions of the world.

FIG. 1.

Aerosol transmission of influenza virus from guinea pig to guinea pig is blocked at 30°C. Titers of influenza virus in nasal wash samples are plotted as a function of the day postinoculation. All experiments were performed at 30°C; the RH condition of each experiment is given in the upper right of each graph. Titers from intranasally inoculated guinea pigs are represented as dashed lines; titers from exposed guinea pigs are shown with solid lines. Squares, diamonds, triangles, and circles refer to individual animals. Exposed and inoculated guinea pigs with like symbols were placed on the same shelf.

FIG. 2.

Guinea pigs housed at 30°C shed influenza virus at titers similar to those for guinea pigs housed at 20°C. Average viral titers in nasal wash samples collected from animals housed at either 30°C (solid line) or 20°C (dashed line) are plotted as a function of the time postinfection. Error bars indicate standard deviations.

FIG. 3.

Contact transmission of influenza virus from guinea pig to guinea pig is efficient at 30°C. Titers of influenza virus in nasal wash samples are plotted as a function of the day postinoculation. The RH and temperature conditions of each experiment are indicated above each graph. Titers from intranasally inoculated guinea pigs are represented as dashed lines; titers from exposed guinea pigs are shown with solid lines. Squares, diamonds, triangles, and circles refer to individual animals. Exposed and inoculated guinea pigs with like symbols were housed in the same cage.