My son is 16 months old and was bitten by a tick a week ago. (I found the tick on his head the next day.) My doctor says he does not want to prescribe antibiotics, because he does not know if my son has Lyme disease since it's too early to diagnose. I feel if I wait that it might be too late. What would you suggest in this situation?

S.B.

I would first like to briefly explain about Lyme disease. This infection is caused by a spiral-shaped bacterium called Borrelia burgdorferi, which is transmitted by an ixodid tick, such as a deer tick. For some 50-70 percent of Lyme disease patients, the first indication of the infection occurs within a week or two of the tick bite: a red, ring-shaped "bull's-eye" rash, which slowly enlarges, leaving a clear center. Patients also often experience fatigue, malaise (feeling ill), headache and joint pains. At this stage, treatment with antibiotics nearly always cures the illness, with little if any chance that the person will later develop serious disease.

Without treatment, the bacteria may disseminate, or spread, throughout the body, weeks to months after infection, resulting in complications involving the heart and nervous system. Antibiotics (given orally or, sometimes, intravenously) are usually effective in most cases of early disseminated disease. After months to years, late disseminated disease can occur, usually resulting in chronic joint disease and/or neurologic problems, such as memory impairment or problems with gait. Treatment is largely successful even in these patients, with most people recovering fully.

Treatment options for symptomatic patients are clear. There are several oral and intravenous antibiotics that are quite effective. However, people who have no signs of symptoms of Lyme disease -- such as your son -- generally should not be treated. Only about 1.5 percent of all individuals with a confirmed ixodid tick bite will develop Lyme disease.

There are many reasons why your son may not be infected. First of all, the tick that bit your son may not have been an ixodid tick. If it was much bigger than a pinhead -- the size of the nymph form of the tick, which nearly always is the source of the infection in the spring and summer -- it was probably not the kind of tick that carries Lyme disease. Second, for infection to occur, the tick has to attach to the person's skin and take in blood. If you only found the tick in your son's hair and it was not attached, again, there is very little risk of infection. Finally, the tick must be attached to the skin for at least 36-48 hours to transmit the bacterium. Since you found the tick the day after the exposure, there probably was not enough time for the infection to be passed to your son. Thus, most experts would agree with your doctor's recommendation not to prescribe antibiotics at this point. Of course, if your son develops any signs of early Lyme disease, he should have treatment. Remember that treatment usually cures Lyme disease, especially in the early stages.