Excerpt from Relapsing Fever

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Background

Relapsing fever is characterized by recurrent acute episodes of fever followed by nonfebrile periods of increasing duration.

Relapsing fever is a disease that is spread by 2 distinct vector families, namely the human body louse (Pediculus humanus) and soft-bodied ticks (Ornithodoros), and is caused by various species of Borrelia. The human body louse spreads Borrelia recurrentis infection. Tick-borne relapsing fever can be caused by a least 15 different Borrelia species. Louse-borne relapsing fever is caused by Borrelia recurrentis. Borrelia turicatae, Borrelia hermsii, Borrelia parkeri, and Borrelia duttonii may cause the tick-borne relapsing fever.

Louse-borne and tick-borne relapsing fevers differ in their epidemiology and must be considered separately. The human body louse transmits an epidemic form and is always associated with B recurrentis, whereas a soft-bodied tick transmits the endemic relapsing fever and may be caused by several different Borrelia species. Borreliae are spirochetes that measure 5-20 µm long by 0.5 µm in diameter. Humans are the only host for louse-borne relapsing fever, whereas small mammals and lizards may serve as the natural reservoir for tick-borne Borrelia species.

Pathophysiology

After exposure from an infected louse or tick, spirochetes enter the skin and gain access to the blood stream. Then, the organism can be found in the spleen, liver, lungs, kidneys, central nervous system, and bone marrow.

In louse-borne relapsing fever, B recurrentis is found almost exclusively in the blood and lymph nodes. Louse-borne spirochetes are transmitted either by the bite of a louse or by inoculation of louse feces. Humans acquire infection when infected body lice are crushed and their fluids contaminate mucous membranes, bite wounds, or other breaks in the skin.

Frequency

United States

Tick-borne relapsing fever is endemic in the western states (ie, states west of the Mississippi River), especially sporadically in mountainous areas or in small familial clusters. Tick-borne relapsing fever caused by B hermsii infections occurs during the spring and summer months.

International

Louse-borne relapsing fever has disappeared in large regions of the world and is an important disease only in northeastern Africa (especially in the highlands of Ethiopia) and in South America.

Mortality/Morbidity

Neurological symptoms have been reported in up to 30% of the patients with relapsing fever and may include coma, meningitis, focal neurologic deficits, and seizures.

• Tick-borne relapsing fever is a serious disease; however, if treated, it has a mortality rate of less than 5%. If acquired during pregnancy, tick-borne relapsing fever poses a high risk of fetal loss (ie, up to 50%).
• The epidemic relapsing fever caused by the louse-borne species, B recurrentis, plagued Asia and Europe during the last century and resulted in an untreated patient mortality rate of up to 40%. People who are native to the endemic areas usually experience a milder form of the disease compared to visitors.
• Antibiotic treatment commonly causes a Jarisch-Herxheimer reaction (JHR) with rigors, fever, and hypotension. It is more severe with the louse-born form treated with penicillin. Pretreatment with steroids does not seem to alter this reaction.

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