infectious diseases
Lyme Disease
Epidemiology of Lyme Disease
Lyme disease was recognized in 1976 because of close clustering of cases in Lyme, Connecticut, and is now the most commonly reported tick-borne illness in the US. It has been reported in 49 states, but>90% of cases occur from Maine to Virginia and in Wisconsin, Minnesota, and Michigan. On the West Coast, most cases occur in northern California and Oregon. Lyme disease also occurs in Europe, across the former Soviet Union, and in China and Japan. In the US, Lyme disease is caused primarily byBorrelia burgdorferiand to a lesser extent byB. mayonii, which has recently been found in the upper midwestern states. In Europe and Asia, Lyme disease is caused primarily byB. afzelii,B. garinii, andB. burgdorferi. Onset is usually in the summer and early fall. Most patients are children and young adults living in heavily wooded areas. Lyme disease is transmitted primarily by 4Ixodesspecies worldwide: I. scapularis(the deer tick) in the northeastern and north central US I. pacificusin the western US I. ricinusin Europe I. persulcatusin Asia In the US, the white-footed mouse is the primary animal reservoir forB. burgdorferiand the preferred host for nymphal and larval forms of the deer tick. Deer are hosts for adult ticks but do not carryBorrelia. Other mammals (eg, dogs) can be incidental hosts and can develop Lyme disease. In Europe, larger mammals such as sheep are hosts for the adult tick. 