There are two forms of relapsing fever, tickborne and louseborne. Both diseases are caused by spiral-shaped species of Borrelia bacteria.
The name relapsing fever comes from the disease cycle – a succession of peaking and waning as the bacterium spreads in a host, is attacked but not eliminated by the immune system, and begins to multiply and spread again. This relapsing cycle can repeat for months if not treated. Though relapsing fever is seldom fatal in humans, it can be very serious and prolonged, particularly for women who are pregnant due to the threat of infection and death of the fetus.
Tickborne relapsing fever can occur anywhere in the world where certain species of soft-bodied ticks, such as Ornithodoros turicata and Ornithodoros hermsi, are found. In the United States, most cases of tickborne relapsing fever occur in the West and are associated with summer cabin vacations. Many cases also are found in parts of Africa.
Soft ticks, unlike hard ticks to which most people are accustomed, usually feed at night and only briefly attach to a host. Their typical blood meals are taken from small animals such as squirrels, mice, and chipmunks, but they also will feed on humans and spread disease. Because their bite is painless, and they only feed for about 15 minutes before returning to their nests, most people never know they were bitten.
The video below shows field work done for research published in November 2012 in PLoS Neglected Tropical Diseases: Endemic Foci of the Tick-Borne Relapsing Fever Spirochete Borrelia crocidurae in Mali, West Africa, and the Potential for Human Infection.
Last Updated June 17, 2014
Last Reviewed June 17, 2014