Q. We recently moved to the Washington area from the Midwest. Before we left, some relatives told us that we should be concerned about Lyme disease. Should we? How big is the risk? How harmful is Lyme disease? Is there a way to prevent it?

A. Lyme disease is on the rise. Since 1982, when the U.S. Centers for Disease Control and Prevention (CDC) started keeping track, it has increased 25-fold. Each year, more than 12,000 Americans develop Lyme disease. To keep from getting it, you can take some preventive steps. You can also try a new vaccine.

Lyme disease is spread by infected deer ticks. However, you don't get Lyme disease from just a simple, quick bite. To spread the infection, a tick needs to feed for 36 hours or more. Symptoms usually develop within a week or two after infection.

The first sign of Lyme disease is a large red rash at the site of the bite. Other symptoms are similar to those presented by the flu: fever, fatigue, headache, muscle ache and joint pains. The trouble with Lyme disease is that it can cause more serious problems weeks to months later. Possible complications include arthritis (especially of the knees), nerve damage (including Bell's palsy, a paralysis of one side of the face) and difficulty concentrating.

The complications of Lyme disease usually respond to treatment with antibiotics. When antibiotic treatment fails, patients can develop long-term disability, though this is rare.

Because the symptoms can resemble those of more common conditions, Lyme disease can be difficult to recognize. Another problem is that in about 20 percent of cases, patients display no symptoms upon becoming infected but are still at risk for developing complications.

The key step in protecting against Lyme disease is to avoid contact with ticks. The peak time of year for contact with feeding ticks is April through July. Ticks like moist, shaded, leafy areas. They also like the grassy shrubs between residential and more wooded areas. To reduce exposure in such areas, wear long-sleeve shirts and tuck pants into socks or boot tops. Insect repellents containing DEET on skin and clothing also helps.

The new Lyme disease vaccine (Lymerix) is recommended for people 15 to 70 years of age who have frequent or prolonged exposure to tick-infested areas. This includes people who have previously had Lyme disease. (Having had it doesn't make you immune from getting it again.) Areas of the United States that have the highest rates of infected ticks are the Northeast and mid-Atlantic areas (Maryland to Massachusetts) and the upper Midwest (Minnesota and Wisconsin).

The vaccine is given in three doses, the last 12 months after the first. The vaccine greatly reduces risk, but does not afford absolute protection.

The main side effect of the vaccine is soreness in the arm, which occurs in about one in four people. Some develop muscle ache, fever and other flu-like symptoms. The vaccine, which is not a live vaccine, does not cause Lyme disease. Some researchers, however, have raised a theoretical concern that the vaccine could somehow trigger an immune response that mimics Lyme arthritis. Although there are no reports of this happening, the CDC recommends against vaccinating people who have Lyme arthritis that is resistant to treatment.

Jay Siwek, chairman of the department of family medicine at Georgetown University Medical Center, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.

Consultation is a health education column and is not a substitute for medical advice from your physician. Send questions to Consultation, Health Section, The Washington Post, 1150 15th St. NW, Washington, DC 20071. Questions cannot be answered personally.