People who experience a second episode of the characteristic Lyme disease bulls-eye rash likely were bitten by another tick, rather than experiencing a relapse of the first infection, suggests a preliminary study presented at the 45th annual meeting of the Infectious Diseases Society of America (IDSA).
The study is the first to evaluate molecular evidence of recurrent Lyme disease.
Lyme disease, the most common tick-borne infection in the United States and Europe, affects nearly 20,000 Americans each year. It is caused by a bacterium, Borrelia burgdorferi, and transmitted to humans by the Ixodes scapularis tick, commonly referred to as the deer tick. The majority of people bitten by ticks and infected with B. burgdorferi develop a distinctive rash, erythema migrans, often characterized by a bulls-eye, that may have a raised center surrounded by a circular, reddish area.
Most people, approximately 95 percent, recover completely and promptly when treated with two or three weeks of antibiotics. Left untreated, the infection usually goes away within a month but untreated patients can relapse and/or develop late complications affecting the joints, heart, or nervous system.
Physicians who treat Lyme disease have noted that patients who are diagnosed and successfully treated once seem more prone to have the infection again, most likely because they live in areas where ticks are prevalent.
It is striking how often re-infection appears to occur, said Robert B. Nadelman, MD, professor of medicine at New York Medical College, Valhalla, and lead author of the study. Our findings support clinical evidence that a surprising number of patients experience more than one episode of Lyme disease and that recurrent infections are unrelated to the original infection.
Skin biopsies of 282 patients diagnosed between 1991 and 2005 with Lyme disease and who had the erythema migrans rash were studied, and 28 were determined to have had exactly two occurrences of Lyme disease (some others had been infected three or four times). In six of those patients, researchers were able to obtain genotype information about the bacteria from skin biopsies, both from the initial and recurring infection site. They determined that, in each case, different genotypes were involved. That means that two different variations of the bacterium caused the infection, which likely is a result of two separate tick bites, Nadelman said.
Our study investigated microbiologic factors related to recurrence of Lyme disease but our findings underscore the importance of preventing exposure to ticks, by covering exposed skin, using tick repellents, and performing self-examination for ticks on a regular basis during the tick season said Nadelman. It appears that even when people have already had Lyme disease, they are not taking sufficient steps to avoid being bitten again.
Co-authors of the study being presented at IDSA by Dr. Nadelman are: K. Hanincova, G. Madison, I. Schwartz, D. Liveris, D. McKenna, J. Nowakowski, S. Bittker, D. Cooper, S. Sandigursky, D. Brisson, D. Holmgren, and G.P. Wormser.