Relapsing fever, also known as typhinia, is an infection caused by certain bacteria in the genus Borrelia. It is a vector-borne disease transmitted through the bites of lice or soft-bodied ticks.

Along with Rickettsia prowazekii and Bartonella quintana, Borrelia recurrentis is one of three pathogens of which the body louse (Pediculus humanus humanus) is a vector. Louse-borne relapsing fever is more severe than the tick-borne variety.^{[citation needed]}

Louse-borne relapsing fever occurs in epidemics amid poor living conditions, famine and war in the developing world. It is currently prevalent in Ethiopia and Sudan.

Mortality rate is 1% with treatment and 30-70% without treatment. Poor prognostic signs include severe jaundice, severe change in mental status, severe bleeding and a prolonged QT interval on ECG.

Lice that feed on infected humans acquire the Borrelia organisms that then multiply in the gut of the louse. When an infected louse feeds on an uninfected human, the organism gains access when the victim crushes the louse or scratches the area where the louse is feeding. B. recurrentis infects the person via mucous membranes and then invades the bloodstream. No animal reservoir exists.

Willy Burgdorfer, an American scientist born and educated in Basel, Switzerland, is an international leader in the field of medical entomology. He is famous for his discovery of the bacterial pathogen that causes Lyme disease, a spirochete named Borrelia burgdorferi in his honor. He was born in 1932.

Dr. Burgdorfer earned his Ph.D. in zoology, parasitology, and bacteriology from the University and from the Swiss Tropical Institute in Basel.

As a research subject for his thesis he chose to study the development of the African relapsing fever spirochete, Borrelia duttonii in its tick vector Ornitnodoros moubata, and to evaluate this tick's efficiency in transmitting spirochetes during feeding on animal hosts. During his college years he was a member of a research team investigating outbreaks of Q fever in various parts of Switzerland and became interested in similar research activities carried out at the Rocky Mountain Laboratory (RML) in Hamilton, Montana, a U.S. National Institutes of Health research facility. He joined RML in 1952 as a Research Fellow, and later became a Research Associate in the USPHS's Visiting Scientist Program. In 1957, he became a U.S. citizen and shortly thereafter joined the RML staff as a Medical Entomologist.