| Relapsing fever | |
|---|---|
| Specialty | Infectious diseases  |
Relapsing fever is avector-borne disease caused by infection with certainbacteria in the genusBorrelia,[1] which is transmitted through thebites oflice,soft-bodied ticks (genusOrnithodoros), orhard-bodied ticks (GenusIxodes).[2][3]
Most infected people develop sickness between 5 and 15 days after they are bitten. The symptoms may include a suddenfever, chills,headaches, muscle or joint aches, andnausea. A rash may also occur. These symptoms usually continue for 2 to 9 days, then disappear. This cycle may continue for several weeks if the person is not treated.[4]
Along withRickettsia prowazekii andBartonella quintana,Borrelia recurrentis is one of three pathogens of which thebody louse (Pediculus humanus humanus) is a vector.[5] Louse-borne relapsing fever is more severe than the tick-borne variety.[citation needed]
Louse-borne relapsing fever occurs inepidemics amid poor living conditions, famine, and war in thedeveloping world.[6] It is currently prevalent inEthiopia andSudan.[citation needed]
Mortality rate is 1% with treatment and 30–70% without treatment. Poor prognostic signs include severejaundice, severe change in mental status, severe bleeding, and a prolongedQT interval onECG.[citation needed]
Lice that feed on infected humans acquire theBorrelia organisms that then multiply in the louse's gut. 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 the mucous membranes and then invades the bloodstream. No non-human animal reservoir exists.[citation needed]
Tick-borne relapsing fever is found primarily in Africa, Spain, Saudi Arabia, Asia, and certain areas of Canada and the western United States. Other relapsing infections are acquired from otherBorrelia species, which can be spread from rodents, and serve as a reservoir for the infection, by atick vector.[citation needed]
B. hermsii andB. recurrentis cause very similar diseases. However, one or two relapses are common with the disease associated withB. hermsii, which is also the most common cause of relapsing disease in the United States. (Three or four relapses are common with the disease caused byB. recurrentis, which has longerfebrile and afebrile intervals and a longer incubation period thanB. hermsii.)[citation needed]
Borrelia miyamotoi, which is transmitted byIxodes ticks, was reported as a cause of tick-borne relapsing fever in 2011.[7][3]
The diagnosis of relapsing fever can be made on blood smear as evidenced by the presence ofspirochetes. Other spirochete illnesses (Lyme disease, syphilis, leptospirosis) do not show spirochetes on blood smears. Although considered the gold standard, this method lacks sensitivity and has been replaced byPCR in many settings.[8]
Relapsing fever is easily treated with a one- to two-week course ofantibiotics, and most people improve within 24 hours. Complications and death due to relapsing fever are rare.[citation needed]
Tetracycline-class antibiotics are most effective. These can, however, induce aJarisch–Herxheimer reaction in over half of those treated, producing anxiety,diaphoresis, fever,tachycardia andtachypnea with an initialpressor response followed rapidly byhypotension. Recent studies have showntumor necrosis factor-alpha may be partly responsible for this reaction.[citation needed]
Currently, no vaccine against relapsing fever is available, but research continues. Developing a vaccine is very difficult because the spirochetes avoid the immune response of the infected person (or animal) throughantigenic variation. Essentially, the pathogen stays one step ahead of antibodies by changing its surface proteins. These surface proteins,lipoproteins called variable major proteins, have only 30–70% of their amino acid sequences in common, which is sufficient to create a new antigenic "identity" for the organism. Antibodies in the blood that bind to and clear spirochetes expressing the old proteins do not recognize spirochetes expressing the new ones. Antigenic variation is common among pathogenic organisms. These include the agents of malaria, gonorrhea, and sleeping sickness. Important questions about antigenic variation are also relevant for such research areas as developing a vaccine against HIV and predicting the next influenza pandemic.[citation needed]
Relapsing fever has been described since the days of the ancient Greeks.[9] After an outbreak in Edinburgh in the 1840s, relapsing fever was given its name, but the etiology of the disease was not better understood for a decade.[9] PhysicianDavid Livingstone is credited with the first account in 1857 of a malady associated with the bite of soft ticks inAngola andMozambique.[10] In 1873, Otto Obermeier first described the disease-causing ability and mechanisms of spirochetes, but was unable to reproduce the disease in inoculated test subjects and thereby unable to fulfillKoch's postulates.[9] The disease was not successfully produced in an inoculated subject until 1874.[9] In 1904 and 1905, a series of papers outlined the cause of relapsing fever and its relationship with ticks.[11][12][13][14]BothJoseph Everett Dutton andJohn Lancelot Todd contracted relapsing fever by performing autopsies while working in the eastern region of theCongo Free State. Dutton died there on February 27, 1905. The cause of tick-borne relapsing fever across central Africa was namedSpirillum duttoni.[15] In 1984, it was renamedBorrelia duttoni.[16] In 1907,Frederick Percival Mackie discovered thathuman body louse can transmitBorrelia recurrentis, which causes relapsing fever as well.[17] The first time relapsing fever was described in North America was in 1915 in Jefferson County, Colorado.[18]
Sir William MacArthur suggested that relapsing fever was the cause of the yellow plague, variously calledpestis flava, pestis ictericia, buidhe chonaill, orcron chonnaill, which struck early Medieval Britain and Ireland, and of epidemics which struck modern Ireland in the famine.[19][20] This is consistent with the description of the symptoms experienced by KingMaelgwn of Gwynedd as recorded in words attributed toTaliesin and with the "great mortality in Britain" in 548 CE noted in theAnnales Cambriae.[21][self-published source]
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