Behind the Forecast: How climate can influence the spread of disease

Listen to Science Behind the Forecast with Meteorologist Tawana Andrew every Friday on 89.3 WFPL at 7:45 a.m.
Listen to Science Behind the Forecast with Meteorologist Tawana Andrew every Friday on 89.3 WFPL at 7:45 a.m.
Published: Mar. 13, 2020 at 8:10 AM EDT
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LOUISVILLE, Ky. (WAVE) - Weather and climate can have an impact on how diseases spread.

Climate influences the distribution of vectors; vectors are organisms that transmit pathogens between humans or from animals to humans.

"The geographic and seasonal distribution of vector populations, and the diseases they can carry, depends not only on climate but also on land use, socioeconomic and cultural factors, pest control, access to health care, and human responses to disease risk, among other factors," according to the Centers for Disease Control and Prevention (CDC).

The World Health Organization (WHO) says that temperature and surface water play a substantial role in how certain diseases spread.

For example, with malaria and dengue fever, mosquitos are vital to their spread. Mosquitos need stagnant water to breed, and the adults need humidity for viability. Warmer air holds much more moisture, thus providing the humidity mosquitoes need but also helping to increase breeding and reducing the virus' maturation period within the bugs. However, very hot and dry weather can reduce mosquitos survival.

Influenza, or the flu, is a viral infection that affects the respiratory tract. Millions of people are affected each year since the flu is very contagious. It can cause dangerous complications like pneumonia in the elderly, children and other vulnerable groups.

The flu has a seasonal cycle; it’s more prevalent in North America during the late fall, winter and early spring. There are a few theories as to why the flu is more common during the colder months. One explanation is that people stay inside more during the winter, which leads to increased disease transmission (think cruises and schools).

Some experts believe that the virus survives better in drier and colder conditions. One study looked at humidity and its effect on the virus’ survival rate. Since the virus is spread from person to person in aerosolized droplets from coughing and sneezing, humidity may affect how long the droplets can stay in the air.

In warmer regions, like the tropics, the flu season is spread out throughout the year; there are sometimes spikes during the rainy season.

Other potential factors that may influence the spread of diseases include urbanization, increased air travel and population density.

Changes in climate, more specifically global temperatures, could lead to a shift in when or if we see continued seasonal spikes in flu numbers. If indoor crowding during the late fall, winter and early spring months is definitively a factor, then warmer weather could reduce this, and potentially, reduce the transmission of the virus.

A 2013 paper found that warm winters are followed by earlier and more severe flu seasons the subsequent year. Some suggest that this happens because fewer people contract the virus, leaving immune systems susceptible.

The impact of weather and climate on the spread of disease still needs a considerable amount of research.

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