Lyme

By Peter Galvin, MD

Lyme disease is the most common tick-borne disease in the U.S. A bite from infected Ixodes scapularis ticks can transmit the bacterium Borrelia burgdorferi, the causative agent of Lyme disease. The first case was reported in 1975 in Lyme, Connecticut. In 2023, the Centers for Disease Control and Prevention (CDC) reported more than 89,000 cases of Lyme disease in the U.S. However, because many cases are not reported or confirmed with blood testing, it is estimated that up to 476,000 people in the U.S. are diagnosed with and treated for Lyme disease each year.

In the U.S., Lyme ticks are most commonly found in the northeastern, mid-Atlantic, and northern midwestern states. Since the ticks feed on deer and other wild animals found in wooded areas, those wooded areas and areas adjacent to them have the highest risk of Lyme disease. Spring and summer months have the highest rates of transmission. Usually, it is the immature ticks, known as nymphs, that bite humans. Adult ticks are much less likely to bite humans. Therein lies one of the problems with recognizing Lyme infection – the nymph ticks are tiny, about the size of a poppy seed, so they are often unseen and may remain attached to a human for an extended period of time. The longer the tick is attached, the higher the risk of infection. This is why most people diagnosed with Lyme do not report a tick bite.

The most common sign of Lyme disease is a rash called erythema migrans, which occurs in 70% to 80% of cases. While classically described as having a bull’s-eye appearance, the rash is more commonly is uniformly red or has increased redness at the center without clearing around it. It appears within one to two weeks following the tick bite and can expand at a rate of one inch per day, sometimes becoming as large as 28 inches across. The rash occurs at the site of the bite. Other flu-like symptoms may develop including fever, chills, headache, and joint pain. If not identified and treated quickly, B burgdorferi can spread to different organs. For example, it can infect the nerves of the face leading to facial muscle paralysis, causing drooping of the mouth and/or eyelid with difficulty closing the eye on the affected side (Bell palsy). It can also infect the heart, causing a dangerously slow heart rate, and the joints, causing arthritis in the knees, or less commonly, in the shoulder, ankle, wrist, and elbow.

Lyme disease can be diagnosed without blood testing in a person who has been in an area known to have Lyme disease and who has a typical rash, symptoms, and a history of a tick bite. If the person has no known history of a tick bite, then confirmatory antibody testing using a blood sample can be helpful. If the antibody test is initially negative, it should be repeated in several weeks. Lyme can be successfully treated with oral antibiotics, usually doxycycline. Cases caught early require two weeks of antibiotics, while later cases may require treatment for up to a month. Severe cases that involve slowing of the heart rate may require hospitalization and intravenous antibiotics.

Lyme disease can be prevented by avoiding wooded areas in spring and summer. For those who must either live in, work in, or visit these areas, loose-fitting, long-sleeved clothes should be worn, EPA-approved insect repellants should be applied, and careful skin inspection should be done regularly. A shower within 2 hours of being outdoors is also recommended. Sometimes, a single dose of doxycycline may be recommended after a high-risk tick bite to prevent Lyme disease.

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