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Infectious Disease and Microbiology – Relapsing Fever
Relapsing fever is a spirochetal infection characterized by recurrent episodes of fever separated by periods of normal temperature. The disease occurs in two major forms: louse-borne (epidemic) relapsing fever and tick-borne (endemic) relapsing fever.
The epidemiology of relapsing fever varies according to the mode of transmission. Louse-borne relapsing fever, caused by Borrelia recurrentis, is strongly associated with poor socioeconomic conditions, overcrowding, war, famine, and natural disasters, which facilitate the spread of body lice. Although uncommon worldwide today, endemic areas persist in parts of Central and East Africa and the Andes region of South America.
Tick-borne relapsing fever has a worldwide distribution but is particularly common in tropical Africa. In the United States, cases occur mainly west of the Mississippi River. In mountainous regions such as California, Utah, Arizona, New Mexico, Colorado, Oregon, and Washington, Borrelia hermsii is the predominant species, whereas Borrelia turicatae is more common in nonmountainous areas of the Southwest.
Risk factors for louse-borne relapsing fever include homelessness and overcrowding. Tick-borne relapsing fever is associated with recreational or occupational exposure to tick-infested environments. B. hermsii infection is frequently linked to exposure to cabins in pine forests, while B. turicatae infection may follow entry into caves or crawling under houses.
Preventive measures focus on control of lice and ticks. In high-risk settings for tick-borne relapsing fever, postexposure prophylaxis with doxycycline may be recommended. A suggested regimen is doxycycline 200 mg orally on the first day followed by 100 mg daily for four additional days.
The pathophysiology differs according to the vector. In louse-borne disease, crushing infected lice releases Borrelia recurrentis, which enters the body through skin breaks or mucous membranes. Tick-borne disease is transmitted through the saliva of soft-bodied ticks during feeding. Because argasid ticks feed rapidly at night and produce painless bites, many individuals are unaware they were bitten.
Fever corresponds to periods of spirochetemia. During afebrile intervals, spirochetes are sequestered within internal organs. Under immune pressure, the organisms undergo antigenic variation and reappear in the bloodstream, producing recurrent febrile episodes.
Relapsing fever is caused by spirochetes of the genus Borrelia. The human body louse (Pediculus humanus corporis) transmits B. recurrentis, causing epidemic relapsing fever. Tick-borne disease is transmitted by soft-bodied ticks of the genus Ornithodoros, which can carry more than 15 pathogenic Borrelia species.
The incubation period is usually around 8 days, ranging from 5–15 days. Illness begins abruptly with fever accompanied by chills, rigors, headache, malaise, arthralgias, diffuse myalgias, lethargy, cough, jaundice, and photophobia. Some patients develop petechial, macular, or papular rashes. Cardiac and neurologic manifestations may occur, particularly in tick-borne disease.
The febrile episode typically ends suddenly after 3–6 days. After an afebrile period lasting approximately 7–9 days, symptoms recur. Louse-borne relapsing fever usually produces one or two relapses, whereas multiple relapses are common in tick-borne disease.
Physical examination may reveal conjunctival injection and edema, hepatomegaly, splenomegaly, diffuse abdominal tenderness, lymphadenopathy, rales, rhonchi, and neurologic abnormalities. Neurologic complications are more common in tick-borne relapsing fever.
The definitive diagnosis is made by demonstrating Borrelia organisms in peripheral blood obtained during febrile episodes. Thick and thin blood smears stained with Giemsa or Wright stain should be carefully examined. Organisms are rarely detectable during afebrile periods. Dark-field microscopy can also identify spirochetes. Polymerase chain reaction testing may be performed on blood samples. Serologic tests may support the diagnosis but have limited sensitivity and specificity.
The differential diagnosis includes malaria, leptospirosis, dengue fever, babesiosis, tularemia, ehrlichiosis/anaplasmosis, rat-bite fever, and typhus, especially during epidemics of louse-borne relapsing fever.
Treatment depends on the type of disease. Louse-borne relapsing fever is treated with a single oral dose of tetracycline 500 mg or doxycycline 100 mg. Tick-borne relapsing fever requires a longer course, typically tetracycline 500 mg orally every 6 hours or doxycycline 100 mg orally twice daily for 7 days.
Patients with meningitis or encephalitis should receive parenteral antibiotics such as penicillin G or ceftriaxone for 10–14 days. Erythromycin may serve as an alternative regimen, particularly for patients unable to take tetracyclines.
A Jarisch-Herxheimer reaction may occur shortly after initiation of antibiotic therapy, especially with penicillin treatment. This reaction results from rapid destruction of spirochetes and may present with fever, hypotension, chills, and worsening symptoms.
Careful follow-up is necessary because relapses are common. Untreated louse-borne relapsing fever has a mortality rate ranging from 4–40%, while untreated tick-borne disease carries a mortality rate of 2–5%.
Major complications include myocarditis with arrhythmias, liver damage, cerebral hemorrhage, acute respiratory distress syndrome, meningitis, meningoencephalitis, cranial neuritis, aphasia, hemiplegia, iridocyclitis, and panophthalmitis.
Relapsing fever is a spirochetal infection characterized by recurrent episodes of fever separated by periods of normal temperature. The disease occurs in two major forms: louse-borne (epidemic) relapsing fever and tick-borne (endemic) relapsing fever.
The epidemiology of relapsing fever varies according to the mode of transmission. Louse-borne relapsing fever, caused by Borrelia recurrentis, is strongly associated with poor socioeconomic conditions, overcrowding, war, famine, and natural disasters, which facilitate the spread of body lice. Although uncommon worldwide today, endemic areas persist in parts of Central and East Africa and the Andes region of South America.
Tick-borne relapsing fever has a worldwide distribution but is particularly common in tropical Africa. In the United States, cases occur mainly west of the Mississippi River. In mountainous regions such as California, Utah, Arizona, New Mexico, Colorado, Oregon, and Washington, Borrelia hermsii is the predominant species, whereas Borrelia turicatae is more common in nonmountainous areas of the Southwest.
Risk factors for louse-borne relapsing fever include homelessness and overcrowding. Tick-borne relapsing fever is associated with recreational or occupational exposure to tick-infested environments. B. hermsii infection is frequently linked to exposure to cabins in pine forests, while B. turicatae infection may follow entry into caves or crawling under houses.
Preventive measures focus on control of lice and ticks. In high-risk settings for tick-borne relapsing fever, postexposure prophylaxis with doxycycline may be recommended. A suggested regimen is doxycycline 200 mg orally on the first day followed by 100 mg daily for four additional days.
The pathophysiology differs according to the vector. In louse-borne disease, crushing infected lice releases Borrelia recurrentis, which enters the body through skin breaks or mucous membranes. Tick-borne disease is transmitted through the saliva of soft-bodied ticks during feeding. Because argasid ticks feed rapidly at night and produce painless bites, many individuals are unaware they were bitten.
Fever corresponds to periods of spirochetemia. During afebrile intervals, spirochetes are sequestered within internal organs. Under immune pressure, the organisms undergo antigenic variation and reappear in the bloodstream, producing recurrent febrile episodes.
Relapsing fever is caused by spirochetes of the genus Borrelia. The human body louse (Pediculus humanus corporis) transmits B. recurrentis, causing epidemic relapsing fever. Tick-borne disease is transmitted by soft-bodied ticks of the genus Ornithodoros, which can carry more than 15 pathogenic Borrelia species.
The incubation period is usually around 8 days, ranging from 5–15 days. Illness begins abruptly with fever accompanied by chills, rigors, headache, malaise, arthralgias, diffuse myalgias, lethargy, cough, jaundice, and photophobia. Some patients develop petechial, macular, or papular rashes. Cardiac and neurologic manifestations may occur, particularly in tick-borne disease.
The febrile episode typically ends suddenly after 3–6 days. After an afebrile period lasting approximately 7–9 days, symptoms recur. Louse-borne relapsing fever usually produces one or two relapses, whereas multiple relapses are common in tick-borne disease.
Physical examination may reveal conjunctival injection and edema, hepatomegaly, splenomegaly, diffuse abdominal tenderness, lymphadenopathy, rales, rhonchi, and neurologic abnormalities. Neurologic complications are more common in tick-borne relapsing fever.
The definitive diagnosis is made by demonstrating Borrelia organisms in peripheral blood obtained during febrile episodes. Thick and thin blood smears stained with Giemsa or Wright stain should be carefully examined. Organisms are rarely detectable during afebrile periods. Dark-field microscopy can also identify spirochetes. Polymerase chain reaction testing may be performed on blood samples. Serologic tests may support the diagnosis but have limited sensitivity and specificity.
The differential diagnosis includes malaria, leptospirosis, dengue fever, babesiosis, tularemia, ehrlichiosis/anaplasmosis, rat-bite fever, and typhus, especially during epidemics of louse-borne relapsing fever.
Treatment depends on the type of disease. Louse-borne relapsing fever is treated with a single oral dose of tetracycline 500 mg or doxycycline 100 mg. Tick-borne relapsing fever requires a longer course, typically tetracycline 500 mg orally every 6 hours or doxycycline 100 mg orally twice daily for 7 days.
Patients with meningitis or encephalitis should receive parenteral antibiotics such as penicillin G or ceftriaxone for 10–14 days. Erythromycin may serve as an alternative regimen, particularly for patients unable to take tetracyclines.
A Jarisch-Herxheimer reaction may occur shortly after initiation of antibiotic therapy, especially with penicillin treatment. This reaction results from rapid destruction of spirochetes and may present with fever, hypotension, chills, and worsening symptoms.
Careful follow-up is necessary because relapses are common. Untreated louse-borne relapsing fever has a mortality rate ranging from 4–40%, while untreated tick-borne disease carries a mortality rate of 2–5%.
Major complications include myocarditis with arrhythmias, liver damage, cerebral hemorrhage, acute respiratory distress syndrome, meningitis, meningoencephalitis, cranial neuritis, aphasia, hemiplegia, iridocyclitis, and panophthalmitis.
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