- Relapsing fever
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Relapsing fever is an infection caused by certain
bacteriain the genus " Borrelia".cite journal |author=Schwan T |title=Ticks and Borrelia: model systems for investigating pathogen-arthropod interactions |journal=Infect Agents Dis |volume=5 |issue=3 |pages=167–81 |year=1996 |pmid=8805079] It is a vector-borne disease that is transmitted through louse or soft-bodied tick bites.cite journal | author=Schwan T, Piesman J | title=Vector interactions and molecular adaptations of Lyme disease and relapsing fever spirochetes associated with transmission by ticks. | journal=Emerg Infect Dis | volume=8 | issue=2 | pages=115–21 | year=2002 | url=http://www.cdc.gov/ncidod/eid/vol8no2/01-0198.htm |pmid=11897061 ]
Louse-borne relapsing fever
Borrelia" recurrentis is the only agent of louse-borne disease. " Pediculus humanus", is the specific vector. Louse-borne relapsing fever is more severe than the tick-borne variety.
Louse-borne relapsing fever occurs in
epidemicsamid poor living conditions, famine and war in the developing world;cite journal |author=Cutler S |title=Possibilities for relapsing fever reemergence |journal=Emerg Infect Dis |volume=12 |issue=3 |pages=369–74 |year=2006 |pmid=16704771] it is currently prevalent in Ethiopiaand Sudan.
Mortality rate is 1% with treatment; 30-70% without treatment. Poor prognostic signs include severe
jaundice, severe change in mental status, severe bleeding, and prolonged QT intervalon ECG.
Lice that feed on infected humans acquire the "Borrelia" organisms that then multiply in the gut of the louse. When an infected louse feeds on an uninfected human, the organism gains access when the victim crushes the louse or scratches the area where the louse is feeding. "B. recurrentis" infects the person via mucous membranes and then invades the bloodstream. No animal reservoir exists.
Tick-borne Relapsing Fever
Other relapsing infections are acquired from other "Borrelia" species, such as "Borrelia hermsii" or "Borrelia parkeri", which can be spread from rodents, and serve as a reservoir for the infection, via a
tickvector. "Borrelia hermsii" and "Borrelia recurrentis" cause very similar diseases although the disease associated with "Borrelia hermsii" has more relapses and is responsible for more fatalities, while the disease caused by "B. recurrentis" has longer febrile and afebrile intervals and a longer incubation period.
Tick-borne relapsing fever is found primarily in Africa, Spain, Saudi Arabia, Asia, and certain areas in the Western U.S. and Canada.
Most people who are infected get sick around 5-15 days after they are bitten by the tick. The symptoms may include a sudden
fever, chills, headaches, and muscle or joint aches, and nausea; a rash may also occur. These symptoms continue for 2-9 days, then disappear. This cycle may continue for several weeks if the person is not treated.cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | pages = pp. 432–4 |edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0838585299 ] Relapsing Fever is easily treated with 1-2 weeks of antibiotics. Most people improve within 24 hours of starting antibiotics. Complications and death due to relapsing fever are rare.
Relapsing fever is a candidate etiology for a mysterious series of plagues in late medieval and early renaissance-era England referred to at the time as
sweating sicknessbut which have not recurred in epidemic form since the 16th Century.
Antibioticsof the tetracyclineclass are most effective, but may induce a Jarisch-Herxheimer reaction, which occurs in over 50% of patients. This reaction produces apprehension, diaphoresis, fever, tachycardia, and tachypneawith an initial pressor response followed rapidly by hypotension. Recent studies have shown that tumor necrosis factor-alpha(TNF-alpha) may be partly responsible for the reaction.
* [http://www.cdc.gov/ncidod/dvbid/RelapsingFever/index.htm CDC: Relapsing Fever]
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