Climate change and infectious diseases

 By Robin Wylie

The incidence of infectious disease has been dramatically reduced over the past century by increasingly sophisticated vaccines. But evidence suggests that climate change could potentially lead to a resurgence of some of the deadliest illnesses on earth…

Many common infectious diseases are known to be affected by climate variation. But those transmitted by insects are particularly sensitive.
One of the diseases most at risk from climate change is malaria. This bacterial infection kills around 429,000 people each year (more than 80 percent of whom are children under five), and although that number is on the decline, there are fears that in the future, climate change could help malaria spread.
Malaria is transmitted to humans by mosquitoes of the genus Anopheles, which are highly sensitive to climatic variations, generally requiring moist conditions, and a temperature of around 25-28 degrees centigrade to breed. Scientists suspect that rising global temperatures could cause the range of Anopheles mosquitoes to expand, and thereby increase the spread of malaria to humans.
One of the places most at risk could be Africa. The continent is already the world’s malaria hotspot, with 92 percent of the world’s malaria deaths occurring there, but a growing number of scientific studies are suggesting that climate change could make malaria matters even worse in Africa.

A female Anopheles albimanus mosquito feeding on a human host (James Gathany/CDC, Wikimedia)

The most recent of these was published this year in the journal The Lancet. In the study, researchers from the Massachusetts Institute of Technology (MIT) and Colombia University aimed to estimate the effect that projected climate change would have on malaria risk in Africa, using a newly-developed malaria transmission simulator combined with reliable climate change projections.
The study concluded that in east Africa, climate change could significantly expand the range of the Anopheles mosquito by the end of the 21st century, thereby increasing the risk of the disease in the region.
This echoes the findings of an earlier study, which concluded that by the year 2080 climate change would lead to a significant increase in the length of the malaria transmission season (LTS) in parts of both eastern and southern Africa. The same study also predicted that other parts of the world would see similar increases in LTS, such as Central America, southern Brazil, and parts of India and Nepal.

Malaria researchers in Kisumu, Kenya (Rick Scavetta/U.S. Army Africa Public Affairs, flickr)

But malaria isn’t the only mosquito-borne disease that risks being exacerbated by a changing climate. Studies have also found that climate variability could also affect the risk of dengue fever, and there are concerns that the same could be true for yellow fever, encephalitis, hantavirus and even ebola.
There are even signs that climate change could already be altering the distribution of some of these diseases. Recent studies have found that some mosquito-borne diseases, including malaria, dengue fever and yellow fever, as well as tick-borne diseases like Lyme disease and tick-borne encephalitis, have begun to spread to higher latitudes, possibly due to increased temperatures.
The spread of insect-borne pathogens is serious enough, but it’s not the only way that climate change could impact human diseases.
Increased precipitation, another likely result of climate change, is believed to increase the spread of waterborne infections, which can cause deadly diarrheal illness and flourish in the wake of heavy rainfalls. And other infectious diseases, such as salmonellosis, cholera and giardiasis, may show increased outbreaks due to flooding and elevated temperature.
Scientists are also concerned that the melting of permafrost soils in polar regions due to climate change could release ancient viruses and bacteria that may be capable of coming back to life.
Last year, an Anthrax outbreak in northern Russia was blamed on unusually warm weather in the arctic circle. Up to 90 people were hospitalized, and a 12 year-old boy died after being infected by the deadly bacteria. It is believed that a reindeer carcass infected with Anthrax was buried deep in the ice, but unusually high temperatures of up to 35 C in the Siberian tundra last summer, caused the carcass to thaw, and Anthrax spores to be released.
With research — and climate change itself — at an early stage, time will be needed to more fully understand the ways in which diseases will respond to our unstable atmosphere. Doing so will form a crucial part of protecting humans from an uncertain climatic future.

SEE MORE: Climate change and migrations in South Africa by Nicholas Newman

about the author
Robin Wylie
Freelance earth/space science journalist. Currently finishing off a PhD in volcanology at University College London.