Lyme chaser

Tufts researcher pursues causes of debilitating disease’s spread

By Pamela H. Sacks



NORTH GRAFTON — Dr. Stephen M. Rich spends much of his time around ticks and mice.

It doesn’t sound like much fun. But Dr. Rich, a geneticist and assistant professor in the infectious disease division at the Tufts University School of Veterinary Medicine, says it’s worthwhile.

In fact, he is embarked on research that could someday bring Lyme disease under control and have important ramifications for controlling other tick-borne pathogens that have a high rate of fatality and are considered likely agents for bioterrorism.

Dr. Rich traces his penchant for working with mice to his study of genetics while a candidate for a master’s degree in zoology at the University of Vermont.

“They’re everywhere and abundant,” he said. “I started studying rats and mice in Maine, how they differed on the Penobscot Bay islands.”

It was the early 1990s, and his research Down East turned out to be a harbinger of where his expertise would take him. The islands, as it happened, were an emerging area for Lyme disease.

Dr. Rich and colleagues from Yale University and the University of California system are now engaged in developing a vaccine for the white-footed mouse, which is a key organism in the cycle that can lead to human infection by a bacterium that causes Lyme disease, which is manifested in flulike symptoms and joint pain.

How the facts surrounding this zoonotic disease — one transmitted from animal to human — were gradually uncovered is “a great detective story,” Dr. Rich said.

In the late 1970s, a group of mothers in Lyme, Conn., noticed a high incidence of juvenile rheumatoid arthritis among their children. They thought it was very odd, and that there had to be a cause.

The women campaigned and got the cooperation of doctors and public health officials, who discovered that the condition was associated with the bite of a tick. Coincidentally, Dr. Andrew Spielman, a mentor of Dr. Rich’s, identified a new species of tick in 1979 on the Massachusetts island of Nantucket.

By 1980, researchers had discovered that the disease was not caused by the tick itself, but by something the tick was transmitting. In the ensuing five years, researchers learned that the culprit was a particular bacterium that was passed in the wild between the white-footed mouse and the new species of tick. In fact, the bacterium moved from tick to mouse to tick to mouse.

Dr. Rich said it is not known whether the bacterium first developed in the mouse or in the tick, but the association is believed to have occurred millions of years ago. Both species are born free of infection. Mice don’t become infected until they are fed on by an infected tick. And ticks don’t become infected until they feed on an infected mouse.

“It’s a chicken-and-egg thing,” Dr. Rich noted.

The tick is known as a “deer tick” because most often a deer serves as a host upon which the adult tick feeds and where it reproduces. It’s a natural, self-perpetuating cycle. It becomes a problem when a person or a domesticated animal inadvertently steps in and becomes a feeding host.

At that point, the tick transmits the bacterium to the human or other host, rather than to another mouse or a deer, as it would in the natural cycle.

As time passed, more and more people were becoming infected with the bacterium on Nantucket, and the condition was gradually spreading to the mainland’s coast. Dr. Rich recalled that in the early 1990s, he saw deer ticks on Crane’s Beach in Ipswich.

How was this happening?

“The deer were spreading them,” he said. And they were hitching rides on birds. “Ticks themselves don’t travel more than three meters in their lifetimes,” he added.

There are now 13,000 to 14,000 cases of human Lyme disease infection reported annually nationwide. Eighty percent to 90 percent of the cases are along the East Coast, with heavy concentrations in New York’s Westchester County and the Connecticut and New Jersey coastal regions. Additionally, Wisconsin has a cluster.

“In 1990-91, you would never have seen these ticks in Grafton,” Dr. Rich said. “They were just along the coast. Later in the 1990s, they moved outside Route 128 and I-495. They’re now at Quabbin and in the Connecticut River Valley. Now, we have ticks on campus with a 40 to 50 percent infection rate.”

Dr. Rich should know. He spends a good deal of time in the early summer, during the nymph season for ticks, collecting the tiny, eight-legged parasites for his research. The best time is at dusk, he said, when temperatures cool. Sometimes, Dr. Rich dons a head lantern to light the way.

He has thousands of ticks in small vials in a refrigerator. He extracts their DNA and then freezes it.

His research, he said, is “about understanding the disease better, the nuts and bolts of how transmission takes place in the wild.” With that information, he and his colleagues are developing a bait-infused oral vaccine to immunize the mice against infection by the ticks, thus ending the cycle.

Experiments in Connecticut over the last several years have not led to a significant reduction in the number of infected ticks, leading researchers to believe that the chipmunk also may be a host.

Additionally, the researchers are working on a vaccine that would prevent ticks from feeding on a host. Dr. Rich said one interesting lead is that for some unknown reason, ticks don’t like cats. Normally, the transmission of the bacterium occurs at the end of the feeding cycle, which takes about 48 hours.

With cats, “they jump off before they get the full blood meal,” Dr. Rich said. The goal is to develop a vaccine that would produce the same reaction in other hosts.

Dr. Rich’s research is aimed at controlling Lyme disease. But that condition can be treated successfully in most people if a course of antibiotics is started soon after the infection occurs. Perhaps more significantly, the research may lead to protection from other tick-borne diseases, such as babesia, which causes symptoms similar to malaria, and encephalitic viruses, which are often deadly.

Dr. Rich, who earned a doctorate in genetics from the University of California, left a post at the University of Rochester to come to Tufts Veterinary School in 1999. Tufts offered him an opportunity to develop his own program, he said. Along with his work on Lyme disease, he is researching malaria prevention.

“Science is a tough field, long hours and not great pay,” he observed. “I thought it would be nice to be doing this work and have some redeeming results come out of it.”