Twice bitten
By Brian Vastag
From San Diego, at a meeting of the Infectious Diseases Society of America
Second episodes of Lyme disease are probably caused by a second tick bite rather than a return of the original illness, according to a first-of-its-kind study.
Lyme disease is the most common tick-borne disease in the United States, infecting about 20,000 people each year. The disease is caused by the bacterium Borrelia burgdorferi, which deer ticks transmit via biting. Victims often develop a distinctive bull’s-eye rash.
A monthlong course of antibiotics generally clears the infection, but physicians have reported patients who, after successful treatment, return some time later with another round of symptoms. The physicians wondered whether the return of the illness signaled a relapse of the initial infection.
To find out, Robert Nadelman and his colleagues at the New York Medical College in Valhalla scanned and compared DNA markers in bacteria found in the first and second rashes of six relapsing patients. In all six cases, the bacteria from the first and second bull’s eye carried different DNA.
Nadelman says the findings mean that “recurrent infections are unrelated to the original,” and instead arise from a second tick bite. “It appears that even when people have already had Lyme disease, they are not taking sufficient steps to avoid being bitten again,” he says.
