The ticks that transmit Lyme disease to people die of dehydration when exposed to a combination of high temperature and lowered humidity, a new USGS-led study has found. In an earlier related study, the researchers found that southern black-legged ticks, unlike northern ones, usually stay hidden under a layer of leaves, where they are less likely to encounter people. The research group, whose findings were published Jan. 11 in the journal PLOS ONE, hypothesizes that southern ticks typically shelter under leaves to retain moisture, and that this behavior is a key reason why Lyme disease is very uncommon in the South.
Lyme disease sickens an estimated 300,000 Americans a year, according to the US Centers for Disease Control and Prevention, making it more common in this country than West Nile virus or any other illness transmitted by insects or arachnids. Black-legged ticks pick up the disease-causing bacteria,
Borrelia burgdorferi
, by biting infected animals, and can then transmit Lyme disease to people in a subsequent bite. The disease causes fever, headache, fatigue, and sometimes a rash. If not treated promptly, Lyme disease can damage the heart, joints and nervous system.
There are big regional differences in Lyme disease prevalence. In 2015 Alabama reported 11 confirmed cases to the CDC from a population of about 5 million people. Vermont, with less than 700,000 residents, had 491 confirmed cases. Just 14 states in the Northeast, Mid-Atlantic and northern Midwest typically account for 95% of all reported Lyme disease cases. Seeking an explanation for this phenomenon, US Geological Survey research ecologist Howard Ginsberg and colleagues at the University of Rhode Island and Michigan State University have been studying the metabolism, life cycle and behavior of black-legged ticks. In 2014 they collected tick larvae from different parts of the Eastern US and found that no matter where they came from, the larvae all live longer in relatively cool temperatures. Longer life spans increase the odds that the ticks will live long enough to first bite an animal carrying