Infectious Disorders.

Lyme disease is a tick-borne zoonosis caused by spirochetes of the genus Borrelia burgdorferi sensu lato.The majority of Lyme disease cases are localized to endemic foci in the United States, Europe, and Asia.In the United States, more than 90% of cases occur in only nine states: New York, Connecticut, New Jersey, Pennsylvania, Massachusetts, Maryland, Rhode Island, Wisconsin, and Minnesota.B. burgdorferi species are transmitted by hard-shelled ticks of the Ixodes complex, for example, Ixodes scapularis in the northeastern and north central United States.Upon infecting humans, B. burgdorferi replicates in the skin and then disseminates via the bloodstream to other organs, leading to extracutaneous disease manifestations.Seventy to eighty percent of Lyme disease patients develop a characteristic skin rash, erythema migrans (EM), at the site of tick feeding. The rash usually appears within days to weeks of the tick bite (range, 3-30 days).The hallmark of disseminated Lyme disease is the appearance of multiple EM lesions. These arise in about 50% of untreated patients with early localized disease. Secondary lesions are similar to the primary lesion, although are generally smaller in size and can appear anywhere on the body.Fever, malaise, myalgias, and arthralgias generally accompany dissemination of the Borrelia infection.Cardiac involvement in Lyme disease occurs in 4% to 10% of untreated patients, usually as varying degrees of atrioventricular heart block.Acute peripheral nervous system disease may take several forms in Lyme disease: cranial nerve palsies (unilateral or bilateral seventh nerve palsy is the most common neurological manifestation), sensorimotor radiculopathies, and mononeuritis multiplex.■ Late manifestations of Lyme disease may occur in the joints, nervous system, and skin. At this stage, joint involvement usually presents as an intermittent, oligoarticular arthritis. The knee is most commonly affected. [ABSTRACT FROM AUTHOR]