Relapsing fever is an acute febrile illness caused by spirochetes of the genus Borrelia. The high fevers of presenting patients spontaneously abate and then recur. This characteristic pattern of remission and relapse not only gives relapsing fever its name but also allows it to be differentiated clinically from other febrile illnesses as it has since the 1840s. Large outbreaks of louse-borne relapsing fever have occurred throughout the past century. These outbreaks usually occur following man-made breakdowns in public health, as typified by the epidemic following World War II that involved about 10 million people.

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.

Tick-borne relapsing fever, caused by Borrelia hermsii, is endemic in the higher elevations and coniferous forests of the western United States and southern British Columbia, Canada. Although many multicase outbreaks of relapsing fever associated with B. hermsii and its tick vector, Ornithodoros hermsi, have been reported, none has been documented in Montana. Patients usually become ill after they have slept in cabins infested with spirochete-infected ticks that feed quickly during the night. The illness has an incubation period of 4 to18 days and is characterized by recurring episodes of fever accompanied by a variety of other manifestations, including headache, myalgia, arthralgia, chills, vomiting, and abdominal pain.

Relapsing fever is a zoonotic disease caused by several species of the spirochaete, Borrelia. It can be transmitted by lice or ticks depending on the species and part of the world in which it occurs.Borrelia recurrentis is confined to the Horn of Africa and causes louse-borne, epidemic relapsing fever. Other species of Borrelia causing the endemic tick-borne variety occur in pockets in Africa, South America, and Asia. Relapsing fever does not occur in the UK. The risk to travellers of acquiring this disease is low, but travellers to endemic areas should be aware of the risk and to try and avoid being bitten by lice or ticks.

Most people who are infected get sick around 5-15 days after they are bitten by the tick. The symptoms may include a sudden fever, chills, headaches, and muscle or joint aches, and nausea; a rash may also occur. These symptoms continue for 2-9 days, then disappear. This cycle may continue for several weeks if the person is not treated. Relapsing Fever is easily treated with 1-2 weeks of antibiotics. Most people improve within 24 hours of starting antibiotics. Complications and death due to relapsing fever are rare.

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.