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Climate Change Will Cause a Serious Tick Up in Lyme Disease


By Scott Barsotti

Heinz College professor Edson Severnini says that climate change will create new public health crises, particularly involving tick-borne illnesses.

While some of the risks associated with climate change are immense, like more destructive hurricanes and rising sea levels, others are quite tiny. 

We’re talking about ticks. The warming climate is creating conditions that are favorable to ticks, which has resulted in a worrying increase in tick-borne diseases, the most common being Lyme disease.

Heinz College professor and environmental economist Edson Severnini has studied this trend with Dr. Igor Dumic of the Mayo Clinic. He believes that what is already observed to be an increase in Lyme disease in North America may soon become a surge. Lyme disease is caused by bacteria and its symptoms include fever, headache, fatigue, and a characteristic “bulls-eye” rash; left untreated, Lyme disease can spread to the joints, heart, and nervous system, creating chronic health problems.

“Assuming a rise in temperature that is commensurate with conservative estimates of climate change and its effects, we predict that the incidence of Lyme disease in the U.S. will increase by about 21 percent by mid-century,” said Severnini. “This is due not only to a larger number of ticks over a wider area, but also a greater availability of hosts.”

In addition to the toll Lyme disease can take on individual patients and families, a large increase in the number of Lyme and other tick-borne illnesses could overwhelm the health care infrastructure, Severnini says, potentially compromising other services provided by hospital and clinics. 

The study—which draws on meteorological data from the National Oceanic and Atmospheric Administration (NOAA) as well as data from the Centers for Disease Control and Prevention (CDC)—notes that ticks’ development, activity, survival, and behavior are all directly influenced by environmental factors like temperature and humidity.

Severnini and Dumic describe the tick life cycle (we’ll spare you the gory details), making special note of the fact that most ticks that transmit diseases to humans are at the nymph stage of development, which are most abundant during the spring and summer months. As those months get warmer—particularly in temperate regions like the American Midwest and Northeast where ticks already thrive—it will mean better conditions for tick nymphs to survive. 

And warmer temperatures mean that people should be concerned even if they don’t live in an area where ticks are common.

 “Climate change is making the natural habitat of areas historically not prone to ticks suitable for them, which expands the area where exposure could happen,” said Severnini. “In addition, people can be exposed when they travel. This is something the public needs greater awareness of.” 

Such awareness could be built through public health campaigns—encouraging people to use repellents when possible and check themselves for ticks after engaging in outdoor activities, for example—as well as more robust training for physicians to ensure they know how to spot symptoms of Lyme disease, according to Severnini. He notes that there is still a worrying amount of misdiagnosis and underreporting; the CDC logs about 30,000 cases of Lyme disease annually, but that only accounts for about 10 percent of the people who contract the disease each year, according to some estimates.

“Beyond Lyme, evidence suggests climate change will cause an increase in other diseases such as malaria, dengue, and West Nile, among others,” said Severnini. “This should be cause for concern from policymakers as well as public health officials and clinicians.”

Severnini suggests that because some of the co-benefits of climate policy spill over into public health, that the health effects of climate change should be accounted for in policy debates.

“Other studies have documented the impacts of climate change on mortality, but there’s still a lot to do regarding morbidity,” he said. “There might be many effects of climate change, such as in the case of expanding habitats suitable for ticks, that manifest indirectly. Our research highlights the effects of climactic changes that are already happening, and has the potential to help public health agencies prepare for the future.”