Entomologist tracking spread of Lyme disease in region

While most people try to avoid the deer ticks that carry Lyme disease, medical entomologist Stephen M. Rich is collecting as many ticks as possible in an effort to track the spread of the disease in New England.

Rich studies tick populations at numerous sites in Massachusetts under an ongoing grant from the National Institutes of Health. Locations range from Cape Cod and the Islands to the Berkshires. He was surprised to find a thriving population of deer ticks halfway up Mount Greylock, one of the coldest areas in the state.

“Deer ticks used to be limited primarily to a 15 mile zone along the coast of New England,” says Rich. “Now they are moving much farther inland as they seemingly adapt to the cold.” This migration accounts for much of the observed increase in Lyme disease cases.

Rich has also received a $40,000 contract to conduct a Lyme disease survey from the New Hampshire Department of Health and Human Services that will begin in July 2007. “This is the first survey of its kind in New Hampshire and comes on the heels of growing concern about the incidence of Lyme disease in that state,” says Rich, assistant professor in the Department of Plant, Soil and Insect Sciences.

A comprehensive survey of deer tick populations is something Rich would like to see happen in Massachusetts. “Through my NIH grant, I have been collecting ticks throughout the Commonwealth, but the goals of this project are based on specific research objectives and not public health surveillance or risk assessment,” says Rich.

According to Rich, Lyme disease is a zoonosis, which means it exists in wild populations. People and their pets are just unfortunate bystanders in the disease transmission cycle. “Epidemiological studies of Lyme disease in people may not reflect true risk,” says Rich. “Studying ticks is a better indicator of the risk of exposure for a given area.”

Ticks are collected using a white linen cloth attached to a wooden dowel that is dragged through the vegetation of the wooded areas they favor. Collected ticks are brought back to Rich’s laboratory and tested for the presence of the spirochete Borrelia burgdorferi, a microscopic, coil-shaped bacteria that causes Lyme disease. “Infection rates in the adult deer tick population are roughly the same across the state, 50 percent on average with a range of 30 to 75 percent,” says Rich.

Rich uses sophisticated laboratory techniques to determine which variant of the bacteria the ticks are carrying. According to Rich, there are at least 17 types of Lyme disease spirochetes, but only four of them are believed to cause disease. “Showing the distribution of the various types can provide more accurate risk information and focus attention on areas with the worst types,” says Rich, who is developing an affordable blood test that will tell human patients whether they have been exposed to infectious or noninfectious Lyme disease.

According to Rich, other pathogens have also been detected in deer ticks, which can carry hundreds of types of bacteria including Anaplasma andBabesia. Testing of the New Hampshire ticks will include these pathogens, which are present in 10 and 25 percent of adult deer ticks respectively. While there are no human blood tests for Anaplasma and Babesia, they are treated with the same antibiotics used for Lyme disease.

“We may find that tick-borne diseases are caused by many factors, with bacteria like Anaplasma, Babesia and Borrelia working alone or paired with any number of other bacteria to cause complex disease,” says Rich.

Rich is also testing ticks collected as part of a grade-school educational program run by Brigham & Women’s Hospital in Boston. The program, funded by the Centers for Disease Control, collects ticks from yards in communities on the North Shore for analysis.

The Rich laboratory also tests ticks submitted by Massachusetts residents for the presence of Lyme disease on a fee-for-service basis. “We started this service in fall 2006 and the response has been overwhelming,” says Rich. “It underscores how people are really anxious to know more about the threats lurking in their backyards.”

More Information

Stephen Rich's laboratory website

July 24, 2007.