Lyme disease still No. 1 vector-borne illness

Washington -- Scientists tracking ticks bearing pathogens employ many of the same techniques used by the crack team of Las Vegas crime scene investigators on the popular television series "CSI," with one important difference.

"Rather than determining whether a drop of blood found at the scene of the crime belongs to suspect A, B or C, we are looking to see if the DNA we extracted from a tick belongs to human pathogen A, B or C," said Richard Dryden, PhD, professor of biology at Washington and Jefferson College in Pennsylvania.

The pathogens he pursues are those that cause Lyme disease, babesiosis and human granulocytic ehrlichiosis, or HGE.

Lyme disease may have been bumped from the headlines by West Nile virus during the past few years, but it is still the most prevalent vector-borne disease in the United States.

The Centers for Disease Control and Prevention found there was a 40% increase in the incidence of Lyme disease, from 17,000 cases in 2001 to 23,763 cases 2002. Preliminary figures for 2003 -- totals have not yet been tallied -- forecast rates at a similar level.

Although the disease rarely causes death, the illness, especially if untreated, can be serious, resulting in facial palsy, meningitis or carditis.

Those bitten by an infected tick may also develop neurologic or joint abnormalities.

Dr. Dryden is beginning a four-year study funded by the CDC to help pinpoint areas in the Eastern United States where ticks are most heavily concentrated. The plan is for localities to take action to get rid of these "hot spots" and inform residents about their risk of contracting a tick-borne disease, said Dr. Dryden.

While all states except Hawaii, Montana and Oklahoma have reported cases of Lyme disease, the disease is most common in Northeast, mid-Atlantic and upper North Central states.

Ninety-five percent of cases were from Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island and Wisconsin.

While there are annual variations in the tick population, there has likely been a real increase in the number of cases, said Paul Mead, MD, a CDC medical epidemiologist.

Greater awareness of the disease and recognition of its characteristic bull's eye rash plus increased development of wooded areas inhabited by the deer and mice that are host to the ticks likely account for the boost in reported cases, said Michael Zimring, MD, director of the Center for Wilderness and Travel Medicine at Mercy Medical Center in Baltimore.

Covering up is key

Prevention is still the name of the game in efforts to control Lyme disease. "People have to wear long sleeves, slacks tucked into socks, light-colored clothes and an application of insect spray containing DEET," said Dr. Zimring. "And once you get out of the woods, take a shower and do tick checks with partners. It could be a lot of fun."

If ticks haven't settled in for longer than 24 hours, or some say 36 hours, it is less likely a person has contracted Lyme disease, said Dr. Zimring.

Dr. Dryden takes pride in the fact that neither he nor any of his tick-collecting team has contracted a tick-borne illness.

The team dresses entirely in white, looking more like house painters than tick hunters, to allow easy tick spotting. Every 15 minutes they check each other for the tiny arthropods.

"In addition, we have duct tape around the cuffs of our long-sleeved shirts and around our socks into which our pants are tucked," Dr. Dryden reported.

One of the ironies is that there are relatively few ticks in and around Washington and Jefferson College's south-central Pennsylvania location, so Dr. Dryden and his team have to travel to reach potential hot spots in their quest for the bacterium Borrelia burgdorferi, which causes Lyme disease.

He is also on the lookout for the hemoprotozoan parasites of the genus Babesia that causes babesiosis. The number of cases of that disease is in the hundreds rather than the thousands, but the disease can be deadly.

HGE, the third disease on Dr. Dryden's list, is a bacterial disease that was first described in 1994. Its symptoms are the same as those of babesiosis -- the seemingly common "flu-like symptoms."