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Borrelia burgdorferi
Lyme disease spirochete

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Taxonomy

Taxonomic lineage

cellular organisms - Bacteria - Spirochaetes - Spirochaetes (class) - Spirochaetales - Spirochaetaceae - Borrelia - Borrelia burgdorferi group - Borrelia burgdorferi

Phylum Spirochaetes

Spirochaetes is unique phylum of bacteria: in addition to a typical bacterial plasma membrane surrounded by a cell wall containing peptidoglycan, they have an outer lipid bilayer membrane, also referred to as an outer membrane sheath. The space between the protoplasmic cell cylinder and the outer membrane sheath is called periplasm, or periplasmic space. Flagella of spirochetes are similar to the flagella of rod-shaped bacteria but are located between the protoplasmic cell cylinder and outer membrane sheath and are referred as periplasmic flagella (PF). Each PF is attached to one end of the cell cylinder and extends toward the opposite end. These flagella unable spirochetes to swim faster in a high-viscosity gel-like medium than in low-viscosity media. For most of the bacteria the situation is reverse. The phylum contains the only class Spirochaetes with single order Spirochaetales. The order includes several important human pathogens such as Leptospira (family Leptospiraceae), Borrelia and Treponema (family Spirochaetaceae).
Treponema pallidum, causative agent of syphilis: taxonomy, history, biology at MetaPathogen

Genus Borrelia

Genus Borrelia was named after French bacteriologist Amedée Borrel (1867–1936) in 1907is. These organisms cause tick-borne and louse-borne relapsing fever in humans and animals. For example, B. hermsii, transmitted by Ornithodoros hermsi ticks, causes relapsing fever in the Western United States, and B. recurrentis causes louse-borne relapsing fever worldwide. B. burgdorferi was isolated from patients with arthritis-like symptoms by Willy Burgdorfer and Alan G. Barbour in 1982, is the etiologic agent of Lyme disease.

Borrelia burgdorferi group

Borrelia burgdorferi group and Borrelia burgdorferi sensu lato are synonyms. Three species of B. burgdorferi cause most human disease: B. burgdorferi sensu stricto, B. garinii, and B. afzelii. B. burgdorferi sensu stricto is the only species associated with human disease in the United States, whereas all three species occur in Europe, and B. garinii and B. afzelii occur in Asia. B. garinii and B. afzelii are antigenically distinct from B. burgdorferi sensu stricto, and these differences may account for the variation in disease symptoms in different geographic regions.

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General information

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Life stages & transmission cycle

Lyme disease transmission cycle

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Borrelia burgdorferi is transmitted to humans by Ixodes ticks. These small, dark-colored ticks have a 2-year life cycle made up of four developmental stages: egg, larva, nymph, and adult. Eggs are laid in spring and hatch into larvae during the late summer. Larvae feed on small animals (usually white-footed mouse, Peromyscus leucopus) and can acquire B. burgdorferi infection at this stage. The larvae then molt into nymphs, which feed again the following spring to early summer and may transmit the infection to the new host including humans and domestic animals. Nymph must feed for 36-48 hours in order totransmit the parasite. Nymphs molt into adult ticks in mid-October and early-November, when the adult female ticks feed again, mainly on large animals such as deer.

Small mammals and some birds, particularly the white-footed mouse, are important in the transmission cycle of B. burgdorferi, because they serve as reservoirs of the pathogen. Although deer is not reservoir-competent (B. burgdorferi does not live in its organism), they also are important in the cycle because as the principal hosts for the adult ticks they provide bloodmeal that is necessary for a female to lay eggs. Eggs are not infected.

Together with Borrelia burgdorferi, ticks can transmit such parasites as Babesia microti (babesiosis) and Anaplasma phagocytophilum (granulocytic ehrlichiosis).

Ixodes scapularis, black-legged tick, deer tick - vector of Lyme disease - life cycle, pictures at MetaPathogen

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Lyme disease

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Diagnostics of Lyme disease

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Treatment of Lyme disease

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References

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