"How many people have said in an email that I was diagnosed with Lyme disease and the picture was of a dog tick" - which doesn't carry Lyme disease, he said.
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Since there is no vaccine and no universally accepted diagnostic test for Lyme disease, prevention and vigilance are the best precautionary measures. The CDC recommends avoided woody and brushy areas if possible, using insect repellents on skin and clothing, and checking yourself, pets and clothing for ticks.
Historically, black-legged ticks actually roamed in a bigger area of the country, according to a 2010 study, but were wiped out of some areas that were deforested. Now, experts expect tick expansion to continue as warming trends help increase their range.
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"Where the climate is conducive we would expect to see continued expansion, but not in places like Colorado or the arid intermountain west because it's too dry," Eisen said.
The behavior of ticks varies based on habitat: southern ticks like to hang out deeper in the leaf litter, and are thus less likely to encounter humans, so people are more likely to get bitten in the north. That may change, however, as the range of the northern ticks stretches southward, Mather said.