Running into Lyme disease.

Most runners are probably no more likely to come into contact with a Lyme disease carrying tick than anyone else, with one exception--runners who take their workouts off road and onto trails in high-risk areas, which include the Northeast and northern Midwest regions. May, June, and July are the months in which risk of exposure to the infected tick is the greatest, and those months probably account for the most miles logged in by the most runners, as compared to any other time of year.

Until now, the only way to reduce your risk of exposure to Lyme disease was to avoid tick-infested areas, use DEET-containing insect repellents, use even more potent insecticides on clothing, and arrange clothing so that ticks have little access to skin (tuck socks into long pants, for instance). Almost none of these standard recommendations hold any appeal to a runner, especially in warm weather. Now, there is an alternative. A new vaccine has just become available to prevent Lyme disease infection. But before you run to your doctor for your dose, listen to the whole story.

Although Lyme disease is a potentially devastating illness with lifelong consequences if not treated, it is not really that easy to get infected, Only about 13,000 people a year contract Lyme disease, as compared to one million new cases of skin cancer each year.

Not only do you have to come into contact with an infected tick, but it must bite you and remain attached to your skin for 48 hours. To suffer any serious consequences, you must also miss noticing the tick, the bull's-eye-shaped rash that follows, and ignore the flu-like symptoms since an early dose of antibiotics can eliminate the problem.

The vaccine itself has some shortcomings. First of all, it has only just become available, so even if you wanted to get vaccinated, you would not be protected for this tick season. The vaccination requires several shots, which need to begin as much as a year ahead of potential exposure. Fifty-percent effectiveness is achieved with the first two shots, given a month apart. Maximum protection is achieved with the third shot given 12 months later. So plan now if you want to establish protection for Lyme tick season next year. Research has not yet determined when booster shots need to be scheduled, but it is likely that they will be needed.

The vaccine does not give complete protection. Studies show that the rate of infection among those vaccinated is about 80% lower than those not vaccinated. According to experts, even if you've been vaccinated, you should take the usual, recommended precautions against exposure. What's more troublesome is that the vaccine may complicate diagnosis for the 20% who become infected despite being vaccinated--they may be less likely to consider the possibility of Lyme disease since they were vaccinated. In addition, people who are at risk for developing rheumatoid arthritis and those with certain heart conditions should not use the vaccine since the vaccine could make their problems worse.

So, if your running takes you off road in the Northeast or northern Midwest, your best protection may still come from being well informed and vigilant during tick season. On the other hand, the vaccine seems to be quite safe for most people, and would certainly be recommended for anyone who works outdoors in heavily affected areas. As is almost always true, medical decisions are a matter of balancing risks. If running is your main chance of exposure, consult your local health authorities for incidence and complete prevention information.

(Centers for Disease Control and Prevention, www.cdc.gov/ncidod/dvbid/ldfacts.htm, New England Journal of Medicine,

RELATED ARTICLE: Headache, fatigue, fever, chills, sore throat, and aching muscles or joints could be written off as the flu in January. The same symptoms should send you to the doctor when experienced during Lyme disease season when you've been outdoors in a Lyme disease region.