Lyme borreliosis is a tick-borne spirochetal bacterial disease caused by Borrelia burgdorferi. Lyme borreliosis is a systemic illness with potential involvement of the skin, neurological, cardiac, and articular systems. It can mimic a variety of other diseases such as juvenile rheumatoid arthritis, multiple sclerosis, and syphilis.

Epidemiology

The disease is the most frequently diagnosed tick-transmitted illness in the United States. The three major geographic loci of Lyme disease in the United States are the Northeast and middle Atlantic coastal regions, the upper Midwest, and the Pacific Northwest. The disease is found in Europe, Australia, the former U.S.S.R., China, Japan, and several African countries. The vector of Lyme disease is the tick, Ixodes dammini, or related Ixodes ticks such as pacificus, scapularis, or ricinus. B. burgdorferi has been found in other ticks such as the Dermacentor variabilis, Amblyomma americanum, and Haemaphysalis leporispalustris; however, transmission has not been proved.

B. burgdorferi has been found in horseflies, deerflies, and mosquitoes, but proof that these insects are possible secondary vectors has not been established. The reservoirs of B. burgdorferi occur in animals parasitized by infected ticks. The Ixodes tick is a three-host tick with a life cycle of 2 years. Adult ticks mate and feed primarily on deer in late fall; the female deposits eggs on the ground, which produce larvae that are active late the following summer. The tiny larvae obtain a blood meal from infected rodents such as white-footed mice, shrews, chipmunks, and squirrels, which are primary reservoirs for B. burgdorferi. Ground foraging birds are also important hosts for the larvae and nymphs.