Relapsing fever

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Relapsing fever is an infection caused by certain Borrelia species, which are spiral-shaped bacteria called spirochetes (see figure How Bacteria Shape Up).

People are infected when they are bitten by an infected tick or come in contact with an infected louse.
People have sudden chills followed by a high fever, severe headache, vomiting, muscle and joint pain, and sometimes a rash.
Symptoms disappear, then return (relapse) several times.
Identifying the bacteria in a sample of blood confirms the diagnosis.
Antibiotics are usually effective.

(See also Overview of Bacteria.)
Several species of Borrelia bacteria cause relapsing fever. A different species of Borrelia causes Lyme disease.
Tick-borne relapsing fever is transmitted by several species of soft ticks. A tick becomes infected when it feeds on rodents (such as chipmunks and squirrels) that carry a species of Borrelia bacteria. The tick spreads the bacteria to a person when it bites.
This fever occurs in the Americas, Africa, Asia, and Europe. In the United States, the disease occurs mainly in the Western states, particularly between May and September. People who sleep in a rodent-infested cabin in the mountains are more likely to be bitten by infected ticks. However, because the ticks feed at night and do not remain attached for very long, people often do not recall a tick bite. People who explore caves (spelunking) are also at risk of infection.
Louse-borne relapsing fever is transmitted by infected body lice. A louse becomes infected when it feeds on a human host who is infected with a species of Borrelia. The louse spreads the bacteria to another person when it is crushed. The Borrelia bacteria are then released on to the person