TYPHUS

acute, infectious series of diseases that are characterized by a sudden onset with headache, chills, fever, and general pains, a rash appearing on the third to fifth day, and toxemia (toxic substances in the blood), and terminating after about two to three weeks. Originally considered a single clinical entity, it is now regarded as a group of closely related diseases caused by different species of rickettsiae (bacteria belonging to the family Rickettsiales) and transmitted to humans by insect carriers under the following general classifications: epidemic (louse-borne) typhus; murine, or endemic (flea-borne), typhus; scrub (mite-borne) typhus, or tsutsugamushi disease; and tick-borne typhus. Epidemic typhus is caused by Rickettsia prowazekii and is conveyed from person to person by the body louse, Pediculus humanus. The louse is infected by feeding upon a human who has the disease. The rickettsial bacteria grow in the epithelial cells lining the louse's gut wall and are excreted in the insect's feces. The infection kills the louse after 12 to 18 days. Man is commonly infected by scratching a louse bite, thus rubbing the louse's infected feces into the wound by abrasion. (Rickettsiae may remain viable and retain their virulence for many days in dried louse feces.) After an incubation period of one to two weeks, an infected person experiences headache, loss of appetite, malaise, and a rapid rise in temperature with fever, chills, marked prostration, and nausea. Four to six days after onset a characteristic rash appears over most of the body. The temperature reaches a maximum range by the end of the first week and is sustained until about the 12th day, when it generally falls rather rapidly, becoming normal in an uncomplicated course about the 14th to 16th day. Depression and weakness may be protracted during the recovery, and the patient's convalescence is slow. In fatal cases of the disease, prostration is progressive, and delirium and coma follow; cardiac failure may be the immediate cause of death. Epidemic typhus has been one of the great disease scourges in human history. It is classically associated with people crowded together in filth, cold, poverty, and hunger; wars and famine; refugees; prisons and jails; concentration camps; and ships. Recognizable descriptions of the disease occur in European literature from the Middle Ages on, and devastating epidemics of typhus continued to occur intermittently throughout Europe in the 17th, 18th, and 19th centuries. Prominent outbreaks occurred during the Napoleonic Wars and during the Irish potato famine of 184649. Epidemic typhus was clearly differentiated as a disease entity from typhoid fever in the 19th century. Major progress in combating the disease began only after 1909, when the French physician Charles Nicolle demonstrated that typhus is transmitted from person to person by the body louse. In the early 20th century typhus decreased and then practically disappeared from western Europe as improvements in living conditions and hygiene occurred. The disease remained intermittently epidemic in eastern Europe, the Middle East, and parts of Africa, however. At the close of World War I the disease caused several million deaths in Russia, Poland, and Romania, and during World War II it again caused epidemics, this time among refugees and displaced persons, particularly in the German concentration camps. A vaccine for typhus was developed during World War II and is effective in greatly alleviating the course of the disease if contracted. The development of the pesticide DDT in the mid-20th century provided an effective means of preventing outbreaks of epidemic typhus, since this chemical is a powerful and long-lasting lousicide. It is applied directly to the clothing of persons at risk and kills the lice as they hatch on the person's body. Like other types of typhus, epidemic typhus can be quickly and effectively treated by chloramphenicol and by the tetracyclines. Despite techniques using vaccination and delousing, typhus is still an ever-present threat to impoverished and destitute peoples in many parts of the world. A condition that is closely related to epidemic typhus is Brill-Zinsser disease, or recrudescent typhus, in which mild symptoms of epidemic louse-borne typhus reappear after a latent period, sometimes of many years, in persons who at one time had contracted epidemic typhus. The disease was first noted when cases of typhus occurred in communities that were free of lice. If treated early with chloroamphenicol or a tetracycline drug, most patients with Brill-Zinsser disease recover. Endemic, or murine, typhus, caused by Rickettsia typhi (mooseri), has as its principal reservoir of infection the Norway rat; occasionally, the common house mouse and other species of small rodents have also been found to be infected. The tropical rat flea Xenopsylla cheopis is the principal carrier of the disease, and transmission to humans occurs through the medium of infected flea feces. The frequency of occurrence of human cases is determined by the amount of contact humans have with domestic rodents. The course of the illness is essentially the same as for louse-borne typhus, but it is milder, complications are less frequent, and the overall fatality rate is less than 5 percent. Scrub typhus (q.v.) is usually classed as a separate disease entity. Tick-borne typhus is also classed as a separate disease called spotted fever (see Rocky Mountain spotted fever).