Structural explanation for the effect of humidity on persistence of airborne virus: seasonality of influenza.

Seasonal variation of infectious diseases is one of the oldest observations in epidemiology, most particularly for Influenza and other respiratory viral infections. The reason for this seasonality is poorly understood, despite the profound importance of these infections as communicable diseases capable of causing global epidemics. Environmental factors including relative humidity, vapor pressure and temperature are known to affect seasonal virus survival and transmission. Immunological status of the host and evolution of the virus have also been proposed to be the reason behind the cyclic recurrence. The molecular basis of these effects or their interplay with biological factors has not been reported before. Here a theoretical analysis shows that the structure of the viral envelope determines its persistence and transmission in various environmental conditions. Physico-chemical properties of the virus particles and their interaction with atmospheric processes along with the availability and susceptibility of hosts generates the conspicuous seasonality prevalent in the temperate zones and the apparent lack of it in the tropics. Additionally this model can estimate virus transmission in different weather conditions. This model may help to determine the right actions effective in preventing outbreaks of the flu-like respiratory viruses.