This Will Tick You Off: Climate Change Is Spreading a Nasty Disease

Lyme is on the rise as infected ticks emerge from hibernation earlier because of global warming.

(Photo: Paul Whitten/Getty Images)

Feb 20, 2015· 2 MIN READ
Melanie Haiken is a San Francisco Bay Area–based health, science, and travel writer who contributes regularly to Forbes.com and numerous national magazines.

Bears aren’t the only critters emerging from hibernation earlier than ever as temperatures rise.

Thanks to climate change, tick season will arrive prematurely this year and be more dangerous, according to a new report. That's because changing weather patterns are making conditions more comfortable for black-legged ticks, the pests that carry Lyme disease.

Little known before the 1980s, Lyme disease is much more serious than most people realize, experts say. While those who catch it early suffer what feels like a bad flu, others have lifelong complications. Long-term neurological issues include numbness, pain, and stiffness in the arms and legs, tremors, facial paralysis, and vision problems. Some people have nerve damage, memory problems, and other cognitive issues that may turn up years later.

Researchers at the Cary Institute of Ecosystem Studies in Millbrook, New York, (ground zero for Lyme disease) looked at almost 20 years of data and concluded that ticks are emerging from their winter sleep earlier. They are also changing their reproductive cycle in worrisome ways as a result of warming temperatures.

"Ticks are emerging earlier as the climate warms—as much as three weeks earlier in warmer years," said Richard Ostfeld, a Cary Institute disease ecologist and coauthor of the research, which appears in a special issue of the journal Philosophical Transactions of the Royal Society B.

Such knowledge allows people to be on the lookout for ticks, Ostfeld said, "rather than getting blindsided thinking they're still safe for a few more weeks." Experts are wondering whether it's time to move Lyme Disease Awareness Month from May to April.

This is not good news for folks in the Northeast, Midwest, and other parts of the country where Lyme disease is already a major health threat. According to Centers for Disease Control and Prevention statistics, cases of Lyme disease rose 25 percent nationwide between 2012 and 2013, with 27,200 cases diagnosed last year alone. But the reality is much worse—only 10 percent of cases are reported, and CDC estimates of cases are as high as 300,000.

The primary sign of Lyme disease—a rash or red ring around the bite—can be hard to see and isn't present in some cases. The only way to prevent the disease is to stay out of the ticks' way, said Ostfeld, which is why their early arrival is so problematic. "Anticipating the peak is very important because there is little we can do to prevent Lyme disease besides avoidance of ticks," he explained.

The Cary Institute's research, spearheaded by Taal Levi, an assistant professor at Oregon State University, identified another important issue. "In warmer years, more of that year's larvae were feeding before the onset of cold weather in fall," said Ostfeld. "In cooler years, more larvae overwinter and come out in spring, when the nymphs are active. What this means is that a warming climate reduces the overlap between larvae and nymphs." Why does this matter? When tick life stages begin to overlap, it raises the incidence of Lyme. This means that looking ahead, we can expect warmer overall temperatures to lead to more cases of Lyme disease, Ostfeld said.

But aren't the mountains of snow blanketing the East and the Midwest killing off the ticks? No—just the opposite. Between the snow and the ground is a protected layer known as subnivean space that comfortably harbors both ticks and their favorite host, the white-footed mouse. These mice carry the same Lyme-causing bacteria as well as babesiosis and encephalitis.

The threat is spreading. It has appeared on the West Coast, particularly in Northern California, range maps show. Every year, cases are reported in new areas, moving west and south.

That both Lyme-carrying ticks and the disease itself are moving out from their original epicenters in the Northeast and the Midwest has been well established, Ostfeld said, yet it hasn't been clear whether the spread is because of climate change or other factors. "But our review evaluated the evidence and found a clear climate signal."