Relapsing fever

Relapsing fever is an infection caused by certain bacteria in the genus Borrelia.^[1] It is a vector-borne disease that is transmitted through louse or soft-bodied tick bites.^[2]

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Infection

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 epidemics amid poor living conditions, famine and war in the developing world;^[3] it is currently prevalent in Ethiopia and 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 interval on 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 tick vector. 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.

Diagnosis

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.^[4] 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 sickness but which have not recurred in epidemic form since the 16th Century.

Treatment

Antibiotics of the tetracycline class 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 tachypnea with 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.

See also

• Lyme disease
• Typhus

References

External links

• Relapsing+fever at eMedicine Dictionary
• CDC: Relapsing Fever