Definition of Relapsing fever:

Relapsing fever is an infection transmitted by a louse or tick. It is characterized by repeated episodes of fever.

Causes, incidence, and risk factors:

Relapsing fever is an infection caused by two similar bacteria in the Borrelia family. They are called Borrelia recurrentis and Borrelia duttoni.

There are two major forms of relapsing fever:

• 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 United States and Canada.
• Louse-borne relapsing fever (LBRF) is transmitted by body lice and is most common in Asia, Africa, and Central and South America.

Sudden fever occurs within 2 weeks of infection. In LBRF, the fever usually lasts 3-6 days and is usually followed by a single, milder episode. In TRBF, 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 people.

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 liver (hepatitis). Widespread bleeding and pneumonia are other complications.

In the United States, 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 Borrelia 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. It is currently seen in Ethiopia and Sudan. Famine, war, and the movements and groups of refugees often result in epidemics of LBRF. The largest epidemics of LBRF during this century occurred during the World War I and II. At least 1 million people died during these epidemics.