But warm winter has kept deer ticks active
KINGSTON, R.I. — March 7, 2002 — If the drought currently affecting Rhode Island and other northeastern states continues into early summer, then the risk of contracting Lyme disease could decline dramatically in 2002.
According to Thomas Mather, professor of entomology at the University of Rhode Island and director of the URI Center for Vector-Borne Disease, Lyme disease risk depends on the soil moisture levels in June and July. So despite speculation to the contrary, the drought over the last six months is not likely to have an affect on the summer deer tick season unless it continues into mid-summer.
“Ticks are very well adapted to various weather conditions, so they aren’t likely to be impacted by extreme weather during the winter or spring,” said Mather. “They are, however, impacted by soil moisture levels during their active season, so if the dry weather continues it may be a lower year for ticks and their associated infections.”
While the drought hasn’t affected the ticks this winter, the warm weather has. Deer ticks in Rhode Island have remained unusually active throughout the winter months. One day in late February when the temperature approached 50 degrees, Mather collected more than 300 adult ticks in about one hour.
“The warm winter has meant that people have seen ticks all season long,” he said, “but that doesn’t mean that those ticks wouldn’t have been there if it was a cold winter. The ticks just wouldn’t have been as active or visible. It’s their activity level that’s affected by the weather, not their population.”
Mather has been monitoring deer tick populations at 80 sites in Rhode Island since 1993. During the first six years, he found a strong correlation between annual rainfall and tick abundance. But following the 1999 drought, which he called “a catastrophic event for ticks,” deer tick populations changed their pattern and have not fully recovered.
This year Mather plans to closely monitor soil moisture levels to try and assess the threshold at which ticks don’t recover. “It’s sort of like a wilting plant,” he explained. “There’s a point beyond which, even if you give it adequate water, a plant won’t recover. We want to find that point for ticks.”
Once he identifies that threshold, Mather will be able to create a model to provide a weekly forecast of tick activity levels and Lyme disease risk.
In addition to Lyme disease, deer ticks also carry a malaria-like protozoan that causes babesiosis and a bacterium that causes human granulocytic ehrlichiosis (HGE). Like Lyme disease, these infections cause flu-like symptoms, are difficult to diagnose, and can be fatal.
For Information: Thomas Mather 874-5616, Todd McLeish 874-7892