Most people are not yet "tick-literate," Mather said. He regularly gets emails, he said, that say, "‘Oh, my doctor says it can't be a deer tick because it doesn't occur here.' Doctors who are not entomologists don't consider Lyme disease if they believe that vector ticks aren't present."
That's troubling because effective treatment of the disease requires a quick response. But equally troubling is that some people are mistakenly treated for Lyme disease. While TickSpotters has received over 20,000 submissions over two years, over 50 percent wrongly identify the tick in the picture.
"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.
Although Lyme is the most prevalent disease caused by blacklegged ticks, they can also carry Human Anaplasmosis, Babesiosis and Powassan disease.