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Friday, June 20, 2014

Risk of tick encounters this summer remains high

URI researcher says harsh winter was no match for deer ticks

KINGSTON, R.I. – As spring becomes summer this week, those frozen polar vortex days of January and February 2014 are now mostly a faded memory. But it was just a few short months ago when there was a great deal of hopeful thinking in Rhode Island and across America that the frigid winter temperatures would mean fewer ticks this summer. 

The University of Rhode Island’s tick expert, Tom Mather, doesn’t like bursting bubbles, but he says that it just doesn’t seem to be the case. Mather is director of the URI Center for Vector-Borne Disease and its popular TickEncounter Resource Center. This week, his team of researchers are reporting that, even though many people may have trouble noticing the tiny, poppy seed-sized nymph deer tick, there are “really a lot of them out there right now” – in the woods, at campsites, along trails, and in people’s yards. 

In its 21st iteration, the statewide TickEncounter Risk Survey for Rhode Island is showing that nymphal deer tick counts, so far, are running only about 5 percent lower than at this same point in the 2013 survey, but are still 85 percent higher than average over the past 5 years.

“Looking at our full 20-year data set, we had back-to-back, record-breaking years for nymphal deer ticks in 2012 and 2013, and this year the counts are still exceptionally high,” Mather explained. “When tick counts are this high, it usually means there’ll be a higher than average occurrence of tick-borne diseases including Lyme disease, human babesiosis, and anaplasmosis.” 

Mather stresses that even if you aren’t seeing many ticks -- they’re abundant but tiny – it is still especially critical to take tick bite precautions like wearing tick repellent clothing with Permethrin, having the shady perimeter of your yard treated with an effective tick killer, and keeping your pets protected by using tick knockdown products every month. URI’s TickEncounter website is loaded with user-friendly ideas on staying “TickSafe.”

To better understand and predict the risk for contracting a tick-borne disease, Mather and colleagues, including former graduate student Kathryn Berger, examined the year-to-year variability in seasonal nymphal deer tick abundance using 14 years of the survey results. They looked at a number of variables but zeroed in on atmospheric moisture—specifically, relative humidity. 

“While most people find high humidity uncomfortable, deer ticks love it,” Mather said. “They thrive when humidity is above 82 percent in the shady leaf litter habitat they call home, and start dying when there are episodes of sub-82 percent humidity that last longer than 8 hours.” 

Their work was recently published in the journal Parasites and Vectors

In their study, the scientists were able to demonstrate for the first time an ability to “predict total [nymphal deer] tick abundance for the year by calculating the number of moisture limiting events early in the life cycle of the tick.” The incidence of Lyme disease and other deer tick transmitted infections is directly related to the summertime abundance of nymphal stage deer ticks. 

“So far this spring, conditions mostly have been cool and humid, pretty perfect for tick survival,” said Mather. “It could still heat up and turn more consistently drier, and if it does the risk for a dangerous tick encounter will start to drop.” 

Mather’s rule of thumb for Rhode Islanders: “if it’s great beach weather for you, it’s likely hard on ticks.” 

Click here to view 20 years of results from the 
TickEncounter Risk Survey.