Professor hypothesizes level of humidity predictor for ticks

11/07/08 - While a tick forecast in the morning news may sound like another gimmick, University of Rhode Island Professor of Entomology Thomas Mather has possibly discovered a method for predicting tick numbers based on humidity levels.Mather said while URI's more rural campuses are not at high risk for tick encounters, he did point out that South County has one of the highest rates of tick bites in the country.

"Our working hypothesis right now is that tick activity is really dependent a critical [on a] threshold of relative humidity," Mather said. "We did an experiment in the laboratory and it conclusively showed ... they just can't stand low humidity."

In 2006 alone, he said, his vector-borne disease center estimated more than 700,000 people in Rhode Island were at risk of encountering a deer tick where they live.

Mather said he and his researchers have observed that deer ticks are evolved to withstand humidity below 85 percent for about eight hours, and any time after that they usually die.

This hypothesis was first tested in the laboratory and then later in nature. Mather had a graduate student use specialized equipment to collect humidity data hourly in 18 different locations during the course of two years, which confirmed the results of the lab experiment.

The averages of the data showed 10 a.m. to 6 p.m. were the hours where the relative humidity was usually less than 85 percent.

"Eighty-five percent and eight hours seems to be the critical threshold," he said.

Mather cited this year as an example, although he said not all the data has come in yet. This year, he said, Rhode Island experienced two or three consecutive days early in May that read less than 85 percent relative humidity during the entire three-day period. This year he said deer tick numbers are much lower than previous years, and he attributes this to the low humidity early in the season.

"That may have been enough to become detrimental to some of these nymph ticks [baby ticks], just at the time of year when they were coming out," Mather said. "So we may have lost a slug of them, and once you lose them, it's not like they come back."

Mather emphasized this is still all observation and theory, but he believes this is a key factor in determining a tick bite risk level based on humidity data.

"What a public service that would be if we could know this relationship for sure," he said. "That's my goal, is to have basically ... an environmentally driven predictor of tick activity that could be integrated into some kind of [daily reported] index."

He added it is not hard to prevent tick bites, as permethrin-based tick repellent has become extremely effective and user friendly.

"You can actually apply that to clothing, and it'll survive washing even for a couple of weeks," Director of Medical Services at Health Services Dr. Fortunato Procopio said. "Say you're a kind of person who likes to do hiking, likes to be outdoors or maybe you're in environmental sciences and you have to be outdoors," he said. "You could use this permethrin on those items of clothing that you'd be out wearing. It's a pretty dang good repellent."

Procopio said prevention is the best defense against deer tick transmitted diseases, especially when it comes to Lyme disease. He said because a patient in the early stages of Lyme disease exhibits symptoms that are not so different from that of a flu, it is difficult for early detection.

There are tests for Lyme disease, but they take longer to show results than the gestation period of the bacterium, and are not always accurate.

"Someone says, 'I've been bitten by a tick and I want to be treated,'" he said. "If you think you might have Lyme disease, go talk to your physician, because if [they] believe it's Lyme disease, he or she is going to treat you without doing a test."

Procopio said this is not a good thing, as the treatment involves 14 to 21 days of antibiotics. Heavy antibiotic use over time can immunize bacteria, rendering the medicine useless later on, so doctors are not prescribing them frivolously.

Procopio emphasized, again, that prevention is the best medicine.

"If you're living in Southern Rhode Island, you want to take precautions to avoid ticks," he said. "We have close to the second highest [infection rate] of Lyme disease in the country.