Читать книгу Principles of Virology, Volume 2 - Jane Flint, S. Jane Flint - Страница 50

Model for the effect of humidity on the transmission of influenza virus. (Top) Virus particles can be contained in airborne aerosols that are produced from coughs or sneezes. The water in these small droplets evaporates, concentrating the particles into droplet nuclei (defined as droplets <5 mm in diameter and so small and light that they may remain suspended in the air for several hours). (Bottom) Transmission efficiency at 20°C (dashed line) or 5°C (solid line) is shown as a function of percent humidity. At 20°C, transmission is highest at low humidity, conditions that favor conversion of exhaled droplets into droplet nuclei. Reduced particle stability at intermediate humidity is the cause of poor transmission. At high humidity, the conversion from droplets to droplet nuclei is inhibited, and the heavier droplets fall from the air, reducing transmission. At 5°C, transmission is more efficient than at 20°C, but there is a gradual loss of transmission with increasing humidity, presumably also as a consequence of the reduced formation of droplet nuclei. Adapted from Lowen AC et al. 2007. PLoS Pathog 3:1470–1476, under li cense CC BY 4.0. © 2007 Lowen et al.

Seasonality is a familiar feature of influenza: in temperate climates, the infection occurs largely from November to March in the Northern Hemisphere and from May to September in the Southern Hemisphere. There have been many hypotheses to explain this seasonality, but none were supported by experimental data until a guinea pig model was used to show that spread of the virus in aerosols is dependent upon both temperature and relative humidity.

Transmission experiments were conducted by housing infected and uninfected guinea pigs together in an environmental chamber. Transmission of infection was most effective at humidities of 20 to 35%, and blocked at a humidity of 80%. In addition, transmission occurred with greater frequency when guinea pigs were housed at 5°C than at 20°C. The authors conclude that low temperature and humidity, conditions found during winter, favored influenza virus spread. The dependence of influenza virus transmission on low humidity might be related to the size of the droplets produced by coughing and sneezing.