(also called louse-borne typhus), an acute infectious rickettsial disease of man. The causative agent is Rickettsia prowazekii. The source of the disease is an infected person whose blood contains the causative agent. The infected person transmits the disease during the last days of the incubation period, during the period of fever, and until the fifth or sixth day of normal temperature. The vector of the causative agent is lice, generally body lice, which become infected by sucking the blood of an infected person and are capable of spreading the infection five or six days later. Humans become infected after louse feces are rubbed into the skin by scratching or when louse feces come in contact with the mucous membrances. Typhus epidemics have occurred during wars, famines, and other calamities that are accompanied by social distress and by deterioration of sanitary conditions; hence the former names for typhus—war fever and famine fever.

The disease sets in after an incubation period of five to 20 days (average 12 to 14 days), with fever, severe headache, and restlessness. These symptoms are followed four or five days later by a rash that does not spread to the face, lassitude, and stupor or delirium. Serodiagnosis is a valuable means of diagnosing typhus. Treatment includes the use of the antibiotic tetracycline, agents that diminish intoxication, and cardiovascular drugs. A sound diet and good nursing care are also important. The disease recurs in 5–6 percent of the cases.

The principal means of preventing typhus is by controlling lice infestation. Epidemics are halted by early isolation of infected persons, prompt disinfection of the focus of infection, and preventive hospitalization in isolation wards of all infected persons with a temperature. In the USSR, all persons living at the site of an epidemic are kept under medical observation. This includes daily taking of the temperature for 25 days and a weekly examination over a period of 71 days. Immunization with live vaccine is used as an auxiliary measure for the most susceptible groups of the population when there is danger of an epidemic.