Relapsing fevers are acute infections caused by spirochaetes of the genus Borrelia. There are two epidemiological forms: louse-borne relapsing fever, which can be epidemic, is transmitted only between humans by the body louse, whereas tick-borne relapsing fever is a zoonosis and does not appear in epidemics.

The problem in Africa

Louse-borne relapsing fever is endemic in the Sudan, and Rwanda and the highlands of Ethiopia, which are its main endemic focus. LBRF caused world-wide epidemics that affected several million people following the two World Wars (Bryceson et al., 1970). Localized epidemics still occur, as at the end of Ethiopia's civil war. Untreated mortality is high, exceeding 40 per cent in some epidemics; treatment reduces mortality to 1–5 per cent. Refugees, whether from war or disaster, are at high risk.

The organism and its vector

Borrelia recurrentis, a slender, motile, microaerophilic organism, causes LBRF. It is 10–20 microns long, and 0.2–0.5 microns wide, with 4–10 loose coils. It contains 9–11 periplasmic flagellae. Borrelia recurrentis can be grown and propagated in artificial media; its genome is a degraded subset of tick-borne Borrelia duttoni and its genomic errors account for its virulence (Lescot et al., 2008). A variable lipoprotein, structurally homologous to murein lipoprotein of Escherichia coli (Scragg et al., 2000) induces tumour necrosis factor in the reaction to treatment (Vidal et al., 1998).