Definition. Lyme disease was first reported in 1977, following an unusual cluster of adults and children with oligoarticular arthritis in a certain neighborhood of Lyme, Connecticut. Subsequently, a multisystem disease was described and attributed to the spirochete Borrelia burgdorferi. Lyme disease manifests as a spectrum of skin, musculoskeletal, cardiac, and neurologic findings. It is a vector-borne disease following the bite of an Ixodes tick—usually the black-legged Ixodes scapularis, commonly known as the deer tick. The species Ixodes includes additional subspecies (eg, I. pacificus, I. dammini, and I. ricinus) that contribute to a worldwide distribution of the disease and known to be endemic in North and South America, Europe, Asia, Africa, and Australia. Prenatal exposure to B. burgdorferi and the development of gestational borreliosis can result in maternal Lyme disease with placentitis and transplacental infection of the fetus and newborn.
Incidence. In 2006, 19,931 cases of Lyme disease were reported to the Centers for Disease Control and Prevention, an incidence of nearly double that reported in 1991 and 1992. In the United States, 44 continental states reported cases of Lyme disease, with an incidence of 8.2 in 100,000 nationwide. In the 10 northeastern states with greatest disease prevalence, the incidence was 30.2 in 100,000. No specific data for the number of pregnancy related Lyme disease are available; however, for U.S. women in the childbearing age groups 15–19 years to 40–44 years, for the period 1992–2004, the disease incidence was lowest for the 15–19 year old group at 4 in 100,000 and highest for the older group at 8 in 100,000. These data suggest a relatively low exposure to Lyme borreliosis for childbearing women. Estimates for active infection following exposure to a deer-tick bite are only 1–3%. Presumably the number of infected pregnant women in the United States is small.
Transmission. The Ixodes tick lives a 2-year life cycle consisting of three life stages: larval, nymph, and adult. The preferred murine reservoirs for the larval and nymph tick are the white-footed field mouse, and for the adult tick it is the white-tailed deer. The larval stage emerges from eggs in early summer and feeds on previously infected mice from which they acquire the Borrelia burgdorferi spirochete. The infected nymph stage emerges the next spring and is the most likely source of human infection because the activity of the feeding nymph corresponds to the outdoor activity of humans in spring and summer. The adult tick may infect as well before laying eggs in summer and dying soon afterward.
Human spirochetemia. Following the tick bite, the incubation period of the spirochetes is 1–55 days with a median of 11 days, followed by the first clinical signs of disease. The disease is characterized by "early" and "late" manifestations. Early disease is in two stages. Early stage I is confined to reactions in the skin. Early stage II is dissemination of the spirochetes from the site of the bite through the skin and into the bloodstream and organ tissues. Spirochete dissemination ...
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