Lyme Disease

Lyme disease is caused by the bacterium Borrelia burgdorferi and is transmitted to humans by the bite of infected blacklegged ticks. Typical signs include fever, headache, fatigue, and a characteristic skin rash called erythema migrans. If left untreated, infection can spread to joints, the heart, and the nervous system. Lyme disease is diagnosed based on symptoms, physical findings (e.g., rash), and the possibility of exposure to infected ticks; laboratory testing is helpful in the later stages of disease. Most cases of Lyme disease can be treated successfully with a few weeks of antibiotics. Steps to prevent Lyme disease include using insect repellent, removing ticks promptly, landscaping, and integrated pest management. The ticks that transmit Lyme disease can occasionally transmit other tick-borne diseases as well.

Transmission of Lyme Disease

Ticks transmit Lyme Disease. The Lyme disease bacterium, Borrelia burgdorferi, normally lives in mice, squirrels and other small animals. It is transmitted among these animals; and to humans; through the bites of certain species of ticks. In the northeastern and north-central United States, the blacklegged tick (or deer tick, Ixodes scapularis) transmits Lyme disease. In the Pacific coastal United States, the disease is spread by the western blacklegged tick (Ixodes pacificus). Other tick species found in the United States have not been shown to transmit Borrelia burgdorferi. Blacklegged ticks live for two years and have three feeding stages: larvae, nymph, and adult. When a young tick feeds on an infected animal, the tick takes the bacterium into its body along with the blood meal. The bacterium then lives in the gut of the tick. If the tick feeds again, it can transmit the bacterium to its new host. Usually the new host is another small rodent, but sometimes the new host is a human. Most cases of human illness occur in the late spring and summer when the tiny nymphs are most active and human outdoor activity is greatest. Although adult ticks often feed on deer, these animals do not become infected. Deer are nevertheless important in transporting ticks and maintaining tick populations.

Dogs and Cats Do Not Spread Lyme Disease To Humans

Although dogs and cats can get Lyme disease, there is no evidence that they spread the disease directly to their owners. However, pets can bring infected ticks into your home or yard. Consider protecting your pet, and possibly yourself, through the use of tick control products for animals.

Signs of Lyme Disease

The Lyme disease bacterium can infect several parts of the body, producing different symptoms at different times. Not all patients with Lyme disease will have all symptoms, and many of the symptoms can occur with other diseases as well. If you believe you may have Lyme disease, it is important that you consult your health care provider for proper diagnosis.

The first sign of infection is usually a circular rash called erythema migrans or EM. This rash occurs in approximately 70-80% of infected persons and begins at the site of a tick bite after a delay of 3-30 days. A distinctive feature of the rash is that it gradually expands over a period of several days, reaching up to 12 inches (30 cm) across. The center of the rash may clear as it enlarges, resulting in a bull’s-eye appearance. It may be warm but is not usually painful. Some patients develop additional EM lesions in other areas of the body after several days. Patients also experience symptoms of fatigue, chills, fever, headache, and muscle and joint aches, and swollen lymph nodes. In some cases, these may be the only symptoms of infection.

Treatment of Lyme Disease

Most patients can be cured with a few weeks of antibiotics taken by mouth. Antibiotics commonly used for oral treatment include doxycycline, amoxicillin, or cefuroxime axetil. Patients with certain neurological or cardiac forms of illness may require intravenous treatment with drugs such as ceftriaxone or penicillin.

Patients treated with antibiotics in the early stages of the infection usually recover rapidly and completely. A few patients, particularly those diagnosed with later stages of disease, may have persistent or recurrent symptoms. These patients may benefit from a second 4-week course of therapy. Longer courses of antibiotic treatment have not been shown to be beneficial and have been linked to serious complications, including death.

Effects on the Fetus

Studies of women infected during pregnancy have found that there are no negative effects on the fetus if the mother receives appropriate antibiotic treatment for her Lyme disease. In general, treatment for pregnant women is similar to that for non-pregnant persons, although certain antibiotics are not used because they may affect the fetus. If in doubt, discuss treatment options with your health care provider.

Treatment guidelines have been developed by the Infectious Disease Society of America, IDSA Guidelines for Treatment of Lyme Disease.