Lyme disease is caused by spirochetal bacteria from the genus Borrelia. Because of their double-membrane envelope, Borrelia are often mistakenly described as Gram negative despite the considerable differences in their envelope components with Gram-negative bacteria. The Borrelia species that are Lyme-related are collectively known as Borrelia burgdorferi sensu lato, and show a great deal of genetic diversity.
Borrelia burgdorferi sensu lato is made up of 18 closely related species, but only three clearly cause Lyme disease: B. burgdorferi sensu stricto (predominant in North America, but also present in Europe), B. afzelii, and B. garinii (both predominant in Eurasia). Some studies have also proposed B. bissettii and B. valaisiana may sometimes infect humans, but these species do not seem to be important causes of disease.
Read more about this topic: Lyme Disease
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