Borrelia burgdorferi are helical shaped bacteria about 10-25µm long.

Introduction: Lyme disease was named in 1977 when arthritis was observed in a cluster of children in and around Lyme, Connecticut. Other clinical symptoms and environmental conditions suggested that this was an infectious disease probably transmitted by an arthropod. Further investigation revealed that Lyme disease is caused by the bacterium, Borrelia burgdorferi. These bacteria are transmitted to humans by the bite of infected deer ticks and cause more than 16,000 infections in the United States each year.

From left to right: The deer tick (Ixodes scapularis) adult female, adult male, nymph, and larva on a centimeter scale.

Vector: Black-legged ticks (Ixodes scapularis) are responsible for transmitting Lyme disease bacteria to humans in the northeastern and north-central United States. On the Pacific Coast, the bacteria are transmitted to humans by the western black-legged tick (Ixodes pacificus). Ixodes ticks are much smaller than common dog and cattle ticks. In their larval and nymphal stages, they are no bigger than a pinhead. Ticks feed by inserting their mouths into the skin of a host and slowly take in blood. Ixodes ticks are most likely to transmit infection after feeding for two or more days.

Risk: In the United States, Lyme disease is mostly localized to states in the northeastern, mid-Atlantic, and upper north-central regions, and to several counties in northwestern California. In 1999, 16,273 cases of Lyme disease were reported to the Centers for Disease Control and Prevention (CDC). Ninety-two percent of these were from the states of Connecticut, Rhode Island, New York, Pennsylvania, Delaware, New Jersey, Maryland, Massachusetts, and Wisconsin.

Individuals who live or work in residential areas surrounded by tick-infested woods or overgrown brush are at risk of getting Lyme disease. Persons who work or play in their yard, participate in recreational activities away from home such as hiking, camping, fishing and hunting, or engage in outdoor occupations, such as landscaping, brush clearing, forestry, and wildlife and parks management in endemic areas may also be at risk of getting Lyme disease.

Prevention and Treatment: It is important to remember that prevention measures can be effective in reducing your exposure to infected ticks, and most patients can be successfully treated with antibiotic therapy when diagnosed in the early stages of Lyme disease. Search for the topics listed below for more information on the following topics:

• Prevention and Control
• Symptoms
• Treatment
• Vaccination

Other Tick-Borne Diseases: Information about other tick transmitted illnesses like Southern tick-associated rash illness (STARI), Babesia infection, and ehrlichiosis can be found at CDC Health Topics A-Z.

More on the History of Lyme Disease: Early in the 20th century, European physicians observed patients with a red, slowly expanding rash (called erythema migrans or EM), associated this rash with the bite of ticks, and postulated that it was caused by a tick-borne bacterium. Then in the 1940s, similar tick-borne illness was described that often began with EM and developed into multi-system illness. Later that decade, spirochete-like structures were observed in skin specimens leading to the use of penicillin for treatment.

Aware of these findings, a physician in Wisconsin diagnosed a patient with EM and successfully treated it with penicillin in 1969. In the mid-1970s, physicians observed clusters of children with arthritis in and around Lyme, Connecticut. Other clinical symptoms and environmental conditions suggested that this was a distinct illness probably transmitted by an arthropod. Researchers linked the presence of EM rash lesions to preceding tick bites and determined that early treatment with penicillin not only shortened the duration of EM but also reduced the risk of subsequent arthritis.

In 1982, spirochetes were identified in the midgut of the adult deer tick, Ixodes dammini (referred herein by its original name, the black-legged tick, Ixodes scapularis) and given the name Borrelia burgdorferi. Finally, conclusive evidence that B. burgdorferi caused Lyme disease came in 1984 when spirochetes were cultured from the blood of patients with EM, from the rash lesion itself, and from the cerebrospinal fluid of a patient with meningoencephalitis and history of prior EM. CDC began surveillance for Lyme disease in 1982 and the Council of State and Territorial Epidemiologists (CSTE) designated Lyme disease as a nationally notifiable disease in January 1991.

This article acquired from the CDC.