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The Ripple Effect of Climate Change on Epidemic Risk

Patrick Ayscue, DVM
              Patrick Ayscue, DVM
The potential impacts of climate change have returned to headlines in recent weeks as scientists, activists, and policy makers try to understand the possible implications of a warming planet during one of the busiest hurricane seasons on record. While rising temperatures and sea levels are often considered, changing climate patterns can have vast implications for epidemic risk as well.

Hot Breeding Ground

Changes in global climate patterns have been widely discussed; however, increasing temperatures also have implications for risk mitigation and management, including impacts on infectious disease epidemics. With 2016 the hottest year ever recorded and 2017 following suit, we anticipate a continued increase in the distribution of disease vectors, like mosquitoes and ticks, which can spread illnesses such as Zika, yellow fever, and dengue to areas where they previously could not be effectively transmitted.

To-date, the continental United States has evaded large-scale outbreaks of Zika, dengue, and yellow fever, since Aedes aegypti, the mosquito species transmitting these viruses, prefer tropical and subtropical climates. Previously restricted to Southern Florida and the Gulf Coast region, weather patterns have caused the mosquito’s range to expand, and isolated populations have been identified as far north as Washington, DC, in recent years.

Weather Alert

Increases in extreme weather events, as predicted by climate scientists, may also lead to increases in infectious disease outbreaks. Epidemics have previously been seen in the wake of natural disasters, which can lead to displaced and crowded populations, hotbeds for infection transmission. Severe rainfall or flooding is particularly effective at creating environments suitable for the transmission and propagation of infectious diseases such as measles or cholera. Conditions, as currently seen on the devastated island of Puerto Rico, are often more amenable for mosquitoes to breed in flood-affected regions and as a result, may increase disease risk in those areas. 

Even without rising to the level of a natural catastrophe, increased variation in weather patterns can result in changes in human and animal interactions, increasing the potential for zoonotic pathogens to move from animals into human populations. For example, unusually heavy rains may predispose regions to Ebola outbreaks by creating more favorable environments for bats hosting the virus. Similarly, food scarcity brought about by drought, political instability, or animal disease may lead to more bushmeat hunting, raising the risk for Ebola outbreaks. In the American Southwest, years of drought led to booming rodent populations as predators suffered, resulting in deadly hantavirus outbreaks.

Moreover, melting permafrost and ice threaten to reignite long-dormant threats. In August 2016, melting permafrost in Siberia uncovered a nearly century-old reindeer resulting in multiple people becoming infected with anthrax spores associated with the carcass. Genetic fragments of the 1918 Spanish influenza and smallpox viruses have also been found in graves in Alaska and Siberia, raising the specter of the return of some of humanity’s greatest viral enemies.