What causes Lyme disease?
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What causes Lyme disease?
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@callum-1 The species Borrelia burgdorferi sensu lato has three well-characterized groups, as follows:
B burgdorferi sensu stricto
B garinii
B afzelii
B burgdorferi sensu stricto is a broad category of closely related but genetically distinct genospecies that constitutes most North American isolates and is found in Europe as well. B afzelii is found mainly in Europe; B garinii is found exclusively in Europe.These subspecies are associated with different clinical presentations, probably due to genomic variation. Infection with B burgdorferi sensu stricto has a particular predilection to affect joints. In European patients with erythema migrans, B afzelii can be isolated from about 80% of lesions and B garinii from 15%. [12] B afzelii often infects the skin only but may persist in that site, causing various cutaneous manifestations including acrodermatitis chronica atrophicans.
B garinii has some neurotropism and is the isolate that accounts for most cases of lymphocytic meningoradiculitis (Bannwarth syndrome) and white matter encephalitis, which is rare in North America. However, this organism can also cause all the various cutaneous manifestations of Lyme disease.
Other strains, which may be sufficiently different in their genetic structure to be considered separate strains, exist; however, most of these are nonpathogenic to humans. This is an area of active research.
In 2016, Mayo Clinic researchers reported the discovery of a novel species of bacteria, provisionally named Borrelia mayonii, isolated in six patients in the upper Midwest of the US with suspected Lyme disease. Clinically, disease from B mayonii is similar to that from B burgdorferi, except that B mayonii is associated with nausea and vomiting, diffuse rashes, and unusually high spirochetemia. Polymerase chain reaction (PCR) testing targeting the oppA1 gene of B burgdorferi sensu lato proved useful in diagnosis.
B burgdorferi is transmitted by ixodid tick species. In the northeastern and upper midwestern United States, Ixodes scapularis (sometimes termed Ixodes dammini) is the vector. In the northwestern United States, Ixodes pacificus is the vector.