North South Divide

Symptoms of Lyme disease, which is caused by Borrelia burgdorferi bacteria transmitted via tick bites, include fever, headache, fatigue, and rash. Without prompt antibiotic treatment, however, Lyme disease can lead to more serious problems, such as heart, joint and nervous system damage. Blacklegged ticks (pictured) are the most common vector of B. burgdorferi and are prevalent throughout the eastern United States. But, inexplicably, northeastern states report more cases of Lyme disease than the south. Now there’s a clue as to why. Ticks die if exposed to extended periods of heat and low humidity, and researchers discovered that in the south, where temperatures are highest, ticks bury themselves under leaves to retain moisture. While northern ticks also stick to shady areas, crucially they don’t go deep into the leaf layer. Thus, it’s thought that by staying buried, southern ticks don’t come into contact with people as often as their northern counterparts.

Written by Ruth Williams

Ruth Williams

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Ruth is a freelance science journalist based in the US. She's a regular correspondent for The Scientist, and her work has appeared in The Lancet, Nature, Scientific American Mind, BBC Focus and elsewhere. Twitter @rooph

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• Image by Graham Hickling, University of Tennessee
• USGS Patuxent Wildlife Research Center, Woodward Hall–PSE, University of Rhode Island, Kingston, RI, USA
• Image copyright held by the photographer
• Research published in PLOS One, January 2017