What is Louse-borne typhus?

* It is a rickettsial disease with variable onset, but is often characterised by the sudden appearance of headaches, chills, prostration, high fever, coughing and severe muscular pain. A macular eruption (dark spot on the skin) appears on the fifth to sixth day, initially on the upper trunk, which then spreads to the entire body excepting, usually, the face, palms and soles of the feet. The case-fatality rate is between 1% and 20%.

* Cause: The causative agent, Rickettsia prowazekii, is transmitted by the human body louse, Pediculus humanus corporis, which is infected while feeding on the blood of patients with acute typhus fever. (Head lice or pubic lice play no role in transmission.) Infected lice excrete rickettsiae when feeding on a second host. People are infected by rubbing louse faecal matter or crushed lice into the bite wound or through scratching.

* Prevalence: The body louse lives in clothing and multiplies very rapidly under poor hygienic conditions. Lice proliferate rapidly in refugee camps and other crowded, unsanitary conditions and the risk can be expected to increase in rainy seasons, when more clothing and blankets are used.

* Since World War II, large outbreaks of typhus have occurred mainly in Africa, with reported cases coming predominantly from three countries: Burundi, Ethiopia and Rwanda. In Ethiopia, the number of annual cases reported annually has ranged between 7,000 and 17,000 (except in 1979, when a higher number was reported), although most have not been confirmed in a laboratory. In the 1970s, major epidemics which occurred in Burundi and Rwanda were documented by serology and isolation: in 1975 alone, 9,000 cases were reported in Burundi. In 1996, Burundi reported 3,500 cases and that number jumped to 20,000 for the period from January to March 1997.

* Warning signals: Louse-borne typhus should be suspected when people in crowded, louse-infected conditions experience sudden onset of high fever, chills, headaches, general pain and severe exhaustion alternating with agitation, followed on the fifth or sixth day by a macular eruption. Clinical diagnosis may be confirmed by serology.

* Latency and recurrence: Humans are the only reservoir and are responsible for maintaining the infection during inter-epidemic periods. Outbreaks occur in colder areas where people live in crowded, unhygienic, louse-infested conditions. Milder symptoms of louse-borne typhus can occur years after the primary attack (Brill-Zinsser disease).

* Period of communicability: The disease is not directly transmitted from person to person. Patients are infective for lice during the febrile illness and possibly for two to three days after the temperature returns to normal. Infected lice pass rickettsiae in their faeces within two to six days after the blood meal; it is infective earlier if crushed. The louse invariably dies within two weeks after infection; rickettsiae may remain viable in the dead louse for weeks.

* Susceptibility and resistance: Susceptibility is general. One attack usually confers long-lasting immunity.