Lyme disease

Definition

A tick-borne zoonosis caused by spirochete bacteria of the genus Borrelia (primarily B. burgdorferi in North America, B. afzelii and B. garinii in Eurasia), transmitted to humans and other vertebrate hosts through the bite of infected Ixodes ticks. The disease exemplifies a complex enzootic cycle involving small mammals as reservoir hosts and ticks as obligate vectors, with humans serving as incidental dead-end hosts. Early-stage infection typically presents with erythema migrans rash, fever, and malaise; untreated infections may progress to disseminated dermatological, arthritic, cardiac, or neurological sequelae.

Etymology

Named for Lyme, Connecticut, USA, where an unusual cluster of juvenile arthritis cases was investigated in 1975, leading to identification of the tick-borne etiology.

Example

In eastern North America, the black-legged tick Ixodes scapularis acquires Borrelia burgdorferi by feeding on infected white-footed mice (Peromyscus leucopus), then transmits the pathogen to subsequent hosts; risk of human Lyme disease peaks in late spring and early summer when nymphal ticks are most active and human outdoor activity increases.

Synonyms

• Lyme borreliosis
• Borreliosis

Related Terms

• vector
• zoonosis
• Ixodes
• Reservoir host
• Enzootic cycle
• Erythema migrans
• Questing
• Acari

Usage Notes

The term specifically denotes infection with Borrelia burgdorferi sensu lato complex; 'Lyme-like' or 'Lyme borreliosis' may be preferred in European contexts where multiple Borrelia species cause clinically similar disease. 'Chronic Lyme disease' is a contested clinical designation without consensus diagnostic criteria, distinct from post-treatment Lyme disease syndrome. Misidentification of tick species or attachment duration often leads to unnecessary prophylactic treatment; proper tick identification and epidemiological risk assessment are essential for clinical decision-making.