Could climate change lead to chikungunya? Examining the link between climate change and health

Polar bears and penguins aren’t the only species threatened by climate change. Years of research has shown that climate change and global human health are intimately linked. From threatening our food and water supplies, to promoting the spread of infectious and waterborne diseases, the current and potential effects of climate change on global health are diverse and momentous.

Climate change is damaging our food security and water supply

Extreme climate events like droughts, heat waves, and hurricanes are on the rise, and they disproportionately impact the poorest and most vulnerable areas of the world. Over the past 60 years, the frequency of extreme climate events has increased from an average of two per year to six with an estimated 70 percent of these disasters occurring in the developing world. Extreme weather events like droughts threaten the world’s food supply, while increased precipitation and flooding bring pathogens into contact with our crops and water supply.

A mere 1°C rise in temperature can alter crop yields by 17 percent—a fact that may not surprise Californians, who are witnessing the state’s greatest drought in history and whose farmers have lost 17,100 jobs and have taken a US$1.5 billion hit. Changes in temperature and rainfall have also been associated with increased rates of diarrhea and dysentery everywhere from Bangladesh to Ecuador, Botswana to the Pacific Islands.

Warmer temperatures can also accelerate the growth of bacteria and reproduction of parasites, leading to increased transmission of salmonella, gastroenteritis, and other water- and food-borne diseases which can make us sick.

“There must be a focus on health systems – there is massive inequality in health systems throughout the world. Because of this, the loss of healthy life years as a result of global environmental change is predicted to be 500 times higher in Africa than in European nations, despite Africa making a minimal contribution to the causes of climate change.”

Professor Anthony Costello, University College London Institute for Global Health

Climate change is promoting the spread of infectious diseases

Perhaps the most notable and direct connection is the impact of rising temperatures on insect-borne diseases—many of which have historically been seasonal or geographically confined.

It appears that mosquitos and ticks, like most humans, prefer warmer climates. In hot, humid weather, they reproduce faster and bite more often, whereas the winter chill can kill both the insects and their eggs.  As global temperatures continue to rise, disease-carrying insects are expected to shift or expand their breeding and biting grounds, infecting people in new regions and for longer periods of time throughout the year. The pathogens carried by these insects—including bacteria and viruses—are also sensitive to shifting climate patterns, and warmer weather is ideal for their survival, reproduction, maturation, and ultimately their infectivity. The lifespan of a mosquito is only a few short weeks, so the accelerated maturation of a pathogenwithin the insect can have a major impact on the spread of the disease.

Cases of Chagas disease, dengue fever, and chikungunya have recently been reported in the southern United States, while cases of tick-borne encephalitis and Lyme disease are increasing in Europe. Malaria has expanded into higher altitudes in Africa and across the Mediterranean to Greece; this is particularly significant as acquired immunity is common in malaria-endemic countries, meaning that the disease may be more virulent in new territories.

“America's public health is deeply tied to the health of our environment. As our planet becomes more interconnected and our climate continues to warm, we face new threats to our safety and well-being.”

United States President Barack Obama

Global health research and development could help mitigate the impact of climate change on health

The threat posed by the spread of these climate-sensitive diseases is amplified by the lack of drugs, vaccines, and other technologies to address them. Chagas disease is curable if treatment begins early, making rapid diagnosis critical, however, none of the treatments are approved by the US Food and Drug Administration. There are no vaccines for Chagas, chikungunya, or dengue fever, and no treatments for chikungunya or dengue. Resistance to the leading agent in malaria treatments—artemisinin—has been reported in Asia. Leishmaniasis and schistosomiasis, two neglected tropical diseases for which there are no vaccines, are both climate-sensitive, and are endemic in regions of the world considered particularly vulnerable to an outbreak due to poverty, conflict, and mass migration.

Mitigating the risk of climate change will require investment in research and development for neglected, infectious diseases, particularly those that are sensitive to climate change.

Climate change is not on the horizon. It is here. And some of the world’s most vulnerable populations are already feeling its impact. As the world seeks to implement solutions to prevent further environmental damage, we must invest in the tools needed to mitigate and adapt to climate change. The consequences for global health could be monumental if we fail to develop the vaccines, diagnostics, or drugs needed to control and slow the spread of infectious diseases.