Relapsing fever is an infection caused by bacteria in the Borrelia family. There are two major forms. Tick-borne relapsing fever (TBRF) is transmitted by the Ornithodoros tick and occurs in Africa, Spain, Saudi Arabia, Asia, and certain areas in the western US and Canada. Louse-borne relapsing fever (LBRF), which is transmitted by body lice, is prevalent in the developing world (Asia, Africa, and Central and South America).

Within 2 weeks of infection, affected people develop sudden-onset high fever. In louse-borne relapsing fever, the initial episode usually lasts 3-6 days and is usually followed by a single, milder episode. In tick-borne relapsing fever, multiple episodes of fever occur and each may last up to 3 days. Individuals may be free of fever for up to 2 weeks prior to a relapse.

In both forms, the fever episode may end in "crisis," which consists of shaking chills, followed by intense sweating, falling temperature, and low blood pressure -- this stage may result in death in up to 10% of individuals.

After several cycles of fever, some people may develop dramatic central nervous system signs such as seizures, stupor, and coma. The Borrelia organism may also invade heart and liver tissues, causing inflammation of the heart muscle (myocarditis) and inflammation of the liver (hepatitis). Diffuse bleeding and pneumonia are other complications of this illness.

In the U.S., TBRF usually occurs west of the Mississippi River, particularly in the mountainous West and the high deserts and plains of the Southwest. In the mountains of California, Utah, Arizona, New Mexico, Colorado, Oregon, Washington, infections are usually caused by B. hermsii and are often acquired in cabins in forests. It is possible that the risk now extends into the southeastern United States.

LBRF is mainly a disease of the developing world, and it often occurs in epidemics. It is currently prevalent in Ethiopia and Sudan. Famine, war, and the movements and congregations of refugees often result in epidemics of LBRF. The largest epidemics of LBRF during this century occurred during the two world wars. Millions of people were infected in these epidemics, with at least 1 million deaths.

• sudden onset of high fever
• rigors
• headache; neck stiffness
• nausea
• vomiting
• muscle aches (myalgia)
• joint aches (arthralgia)
• bleeding
• seizures
• unsteady gait
• facial droop
• coma
• weakness

Relapsing fever should be suspected in someone coming from an endemic area who has repeated episodes of fever, particularly if fever is followed by a "crisis" stage, and if the person thinks they may have been exposed to lice or soft-bodied ticks.

A blood smear is frequently obtained to see if the organism is present. A culture for this organism is not widely available in most laboratories. Certain blood antibody tests are sometimes used.

The mainstay of treatment is antibiotics -- primarily tetracycline, doxycycline, or penicillin.

The mortality (death) rate for untreated louse-borne relapsing fever ranges from 10-70% and from 4-10% in tick-borne relapsing fever. With early treatment, the mortality rate is reduced to 2-5%. Individuals with coma, myocarditis, liver dysfunction, and pneumonia are at higher risk of death.

• neurologic complications: seizures, weakness, facial droop, meningitis, coma
• myocarditis -- may lead to arrhythmias
• pneumonia
• liver dysfunction
• diffuse bleeding
• Jarisch - Herxheimer's reaction during antibiotic therapy may be fatal in some cases

Notify your medical provider if you are a returning traveler and you develop fever -- there are many different possible infections that will need to be investigated in a timely manner.

Wearing proper clothing and insect repellent will help prevent infection. Lice and tick control in endemic areas is another important public health measure.