VIII.116 - Relapsing Fever

Summary

Relapsing fever is a disease characterized by the occurrence of one or more relapses after the primary febrile paroxysm has subsided. Various types of relapsing fever are caused by blood parasites of the Borrelia group. There are two chief forms of the disease: the endemic, transmitted to humans by various ticks of the genus Ornithodoros, and maintained among a variety of rodents; and the epidemic, caused by a parasitic spirochete, Borrelia recurrentis, which is transmitted by human head and body lice. B. recurrentis is less virulent than the tick-borne forms. Under favorable conditions, mortality is about 5 percent, but in times of distress, as in war or famine, it can reach 60 to 70 percent.

It is also known as famine fever and tick fever, and in the past as yellow fever, because of associated jaundice. The term “relapsing fever” was first used by David Craigie of Edinburgh in 1843. The disease was often, and frequently is still, confused with malaria and typhus, whose symptoms are similar.

Etiology and Epidemiology

Tick-borne relapsing fever is normally contained within the relationship between tick and rodent host; human beings become affected only when they accidentally become involved in that relationship. For example, if human shelters such as log cabins attract rodents, they may in turn become tick habitats. Transmission of relapsing fever is through the infected saliva or coxal fluid of the tick, making it essentially a disease of locality. In the case of louse-borne relapsing fever, the only reservoir of B. recurrentis is human beings, despite the fact that the disease is spread by lice, either in the bite, or by contact with the body fluids of the louse through scratching.