TYPHUS, EPIDEMIC

The word "typhus" comes from the Greek word for "cloudy" or "misty," referring to the lethargic state of mind that occurs in typhus victims. Epidemic, or louse-borne, typhus, is also known as historic typhus, European typhus, jail, war, camp, or ship fever.

Epidemic typhus is caused by Rickettsia prowazekii, a small gram-negative obligately intracellular bacterium. The disease starts with an abrupt onset of symptoms following a one to two week incubation period. Clinical manifestations of typhus include intense headache, chills, fever, and myalgia. A characteristic rash develops on the fourth to seventh day of disease. It first appears on the upper trunk and then becomes generalized, involving the whole body except the face, palms, and soles. As the disease progresses, particularly in untreated patients, significant alterations of mental status, from stupor to coma, are observed. In patients with severe disease, hypotension and renal failure are common. Epidemic typhus is a life-threatening illness even for young, previously healthy persons. Fatal outcomes are observed in up to 40 percent of untreated cases.

Transmission and Epidemiology. Epidemic typhus is a disease of humans. The human body louse Pediculus humanus corporis is responsible for transmission of the agent from human to human. Charles Nicolle (1866–1936) first experimentally established this fact, and he received the Nobel Prize in 1928 for his contributions. Lice acquire rickettsiae while feeding on people infected with R. prowazckii. A person infested with infected lice acquires the bacteria when the lice or the rickettsiae present in the louse feces are rubbed into bite wounds or other skin abrasions. Epidemic typhus commonly occurs in cold climates where people live in overcrowded unsanitary conditions with few opportunities to change their clothes or bathe. Such conditions often occur during war and natural disasters, which typically facilitate louse infestation. The history of typhus is, in fact, largely the history of men in battle. The disease has been credited with deciding the outcome of more battles than any general's best-laid strategy. Epidemic typhus is currently prevalent in mountainous regions of Africa, South America, and Asia.

Recovery from epidemic typhus results in nonsterile immunity, permitting the persistence of R. prowazekii between epidemics. Individuals who have been infected sometimes suffer a relapse in the form of Brill-Zinsser disease, which has the symptoms of classic typhus but is usually milder. In the United States, R. prowazekii is also transmitted by the Orchopeas howarolii fleas of flying squirrels. Persons exposed to infected fleas sporadically acquire an infection that is referred to as sylvatic typhus and is typically milder than classic epidemic typhus.

Diagnosis and Treatment. Diagnosis of epidemic typhus is based on detection of specific antibodies in patient sera. The use of clinical and epidemiological data is necessary to distinguish among classic typhus, Brill-Zinsser disease, and sylvatic typhus. Doxycycline is highly effective for treatment of typhus. Epidemic typhus also responds well to treatment with tetracycline or chloramphenicol antibiotics.

Prevention and Control. Insecticides are used to kill body lice, disinfect louse-infested clothing, and prevent the spread of epidemic typhus. Control requires significant efforts to maintain sanitary conditions and living standards, as well as health education. There is no commercial vaccine for preventing epidemic typhus. Several excellent vaccine candidates have been protective in animal models, however.

Marina E. Eremeeva

(see also: Communicable Disease Control; Rickettsial Diseases; Vector-Borne Diseases )

Bibliography

Walker, D. H., ed. (1988). Biology of Rickettsial Diseases. Boca Raton, FL: CRC Press.

Walker, D. H.; Raoult, D.; Brouqui, P; and Marrie, T. (1998). "Rickettsial Diseases." In Harrison's Principles of Internal Medicine, 14th edition, eds. A. S. Fauci et al. New York: McGraw-Hill.

World Health Organization (1997). Epidemic Louse-Borne Typhus (WHO Fact Sheet No. 162). Geneva: Author. Available at http://www.who.int/inf-fs/en/fact162.html.