Relapsing fever overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Relapsing fever is a bacterial infection caused by several species of spirochete bacteria in the Borrelia family.[1] It is a vector-borne disease that is transmitted through louse or soft-bodied tick bites.[2]
Historical Perspective
Relapsing fever has been described since the days of Hippocrates in ancient Greeks. however, the term relapsing fever was first used by David Craigie to describe an outbreak of the disease in Edinburgh in 1843. Livingston first described tick-borne relapsing fever in 1857.The association between spirochetes and the development of louse-born relapsing fever first described by Otto Obermeier in 1873 after an outbreak in Berlin (1867–1868). Cook, Ross, Milne, Dutton, Todd, Koch, and others studied TBRF extensively throughout southern and eastern Africa in the early 1900s.In 1904, Ross and Milne, while working in Uganda, showed that TBRF was caused by a spirochete in the bloodstream. The role of the human body louse in the transmission of relapsing fever was reported by MacKie in 1907.
Classification
There are two major forms of relapsing fever: ENDEMIC TICK BORNE and EPIDEMIC LOUSE BORNE. TBRF is transmitted by soft body ticks (vectors) from a small mammal reservoir and may be endemic or sporadic. LBRF is transmitted person-to-person by human body lice (vectors) from an infected human reservoir. In the early 1900s, many large epidemics were described, predominantly in Africa, the MiddleEast, India, and China. With improved hygiene, the incidence of epidemic relapsing fever has declined in the 20th century, but the disease continues to be a problem in countries of Africa and South America.
Pathophysiology
After entering the bloodstream, spirochetes replicate extracellularly and remain predominantly in the plasma space. Patients generally remain asymptomatic until high-level spirochetemia (104-108 organisms m!) develops, at which time symptoms begin abruptly. Organisms are cleared predominantly by opsonizing antibodies with resolution of symptoms ( afebrile period), followed several days or weeks later by reemergence of a new antigenic strain, high-level spirochetemia, and recurrence of symptoms. There are multiple genes in the spirochete encoding variable membrane proteins( VMPs). These VMPs determine the antigenic serotype of the organism. At any given time, each spirochete has VMP genes that are expressed and others that are silent. An antigenic switch occurs when a given VMP gene transposes from silent to an expressed locus. This cyclical process of initially effective immune response followed by antigenic variation and immunologic escape is responsible for the relapsing nature of this illness.
Causes
Relapsing fever is a bacterial infection caused by several species of spirochete bacteria in the Borrelia family. TBRF is caused by 8 or more Borrelia species: Borrelia hermsii, Borrelia turicatae, Borrelia parkeri, Borrelia duttonii, Borrelia johnsonii, B miyamotoi. The bacteria species associated with LBRF is Borrelia recurrentis which has a genome so similar to B. duttonii and B. crocidurae (causes of East and West African tick-borne relapsing fever). Louse-borne relapsing fever is more severe than the tick-borne variety. Humans are the sole reservoirs of B recurrentis, while small mammals (eg, pets, ground and tree squirrels, chipmunks) and reptiles (lizards, snakes, gopher tortoises) may serve as a reservoir for tickborne Borrelia species.
Differentiating Relapsing fever from Other Diseases
Epidemiology and Demographics
LBRF is an epidemic disease with a history from Hippocrates' times, whereas TBRF is endemic causing sporadic cases since it depends on the presence of tick reservoirs. TBRF is endemic in the western US, southern British Columbia, plateau regions of Mexico, Central and South America, the Mediterranean, Central Asia, and much of Africa. In the United States, TBRF usually occurs west of the Mississippi River, particularly in the mountainous West and the high deserts and plains of the Southwest. In the mountains of California, Utah, Arizona, New Mexico, Colorado, Oregon, Washington, infections are usually caused by Borrelia hermsii and are often acquired in cabins in forests.LBRF is mainly a disease of the developing world. It is currently seen in Ethiopia and Sudan. It is currently seen in Ethiopia and Sudan. Famine, war, overcrowding, and the movement of refugee groups often results in LBRF epidemics.
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References
- ↑ Schwan T (1996). "Ticks and Borrelia: model systems for investigating pathogen-arthropod interactions". Infect Agents Dis. 5 (3): 167–81. PMID 8805079.
- ↑ Schwan T, Piesman J (2002). "Vector interactions and molecular adaptations of Lyme disease and relapsing fever spirochetes associated with transmission by ticks". Emerg Infect Dis. 8 (2): 115–21. PMID 11897061.