An infective disease of worldwide distribution, the manifestations of which vary in di?erent localities. The causative organisms of all forms of typhus fever belong to the genus RICKETTSIA. These are organisms which are intermediate between bacteria and viruses in their properties, and measure 0·5 micrometre or less in diameter.
Louse typhus, in which the infecting rickettsia is transmitted by the louse, is of worldwide distribution. More human deaths have been attributed to the louse via typhus, louse-borne RELAPSING FEVER and trench fever, than to any other insect with the exception of the MALARIA mosquito. Louse typhus includes epidemic typhus, Brill’s disease – which is a recrudescent form of epidemic typhus – and TRENCH FEVER.
Epidemic typhus fever, also known as exanthematic typhus, classical typhus, and louse-borne typhus, is an acute infection of abrupt onset which, in the absence of treatment, persists for 14 days. It is of worldwide distribution, but is largely con?ned today to parts of Africa. The causative organism is the Rickettsia prowazeki, so-called after Ricketts and Prowazek, two brilliant investigators of typhus, both of whom died of the disease. It is transmitted by the human louse, Pediculus humanus. The rickettsiae can survive in the dried faeces of lice for 60 days, and these infected faeces are probably the main source of human infection.
Symptoms The incubation period is usually 10–14 days. The onset is preceded by headache, pain in the back and limbs and rigors. On the third day the temperature rises, the headache worsens, and the patient is drowsy or delirious. Subsequently a characteristic rash appears on the abdomen and inner aspect of the arms, to spread over the chest, back and trunk. Death may occur from SEPTICAEMIA, heart or kidney failure, or PNEUMONIA about the 14th day. In those who recover, the temperature falls by CRISIS at about this time. The death rate is variable, ranging from nearly 100 per cent in epidemics among debilitated refugees to about 10 per cent.
Murine typhus fever, also known as ?ea typhus, is worldwide in its distribution and is found wherever individuals are crowded together in insanitary, rat-infested areas (hence the old names of jail-fever and ship typhus). The causative organism, Rickettsia mooseri, which is closely related to R. prowazeki, is transmitted to humans by the rat-?ea, Xenopsyalla cheopis. The rat is the main reservoir of infection; once humans are infected, the human louse may act as a transmitter of the rickettsia from person to person. This explains how the disease may become epidemic under insanitary, crowded conditions. As a rule, however, the disease is only acquired when humans come into close contact with infected rats.
Symptoms These are similar to those of louse-borne typhus, but the disease is usually milder, and the mortality rate is very low (about 1·5 per cent).
Tick typhus, in which the infecting rickettsia is transmitted by ticks, occurs in various parts of the world. The three best-known conditions in this group are ROCKY MOUNTAIN SPOTTED FEVER, ?èvre boutonneuse and tick-bite fever.
Mite typhus, in which the infecting rickettsia is transmitted by mites, includes scrub typhus, or tsutsugamushi disease, and rickettsialpox.
Rickettsialpox is a mild disease caused by Rickettsia akari, which is transmitted to humans from infected mice by the common mouse mite, Allodermanyssus sanguineus. It occurs in the United States, West and South Africa and the former Soviet Union.
Treatment The general principles of treatment are the same in all forms of typhus. PROPHYLAXIS consists of either avoidance or destruction of the vector. In the case of louse typhus and ?ea typhus, the outlook has been revolutionised by the introduction of e?cient insecticides such as DICHLORODIPHENYL TRICHLOROETHANE (DDT) and GAMMEXANE.
The value of the former was well shown by its use after World War II: this resulted in almost complete freedom from the epidemics of typhus which ravaged Eastern Europe after World War I, being responsible for 30 million cases with a mortality of 10 per cent. Now only 10,000–20,000 cases occur a year, with around a few hundred deaths. E?cient rat control is another measure which reduces the risk of typhus very considerably. In areas such as Malaysia, where the mites are infected from a wide variety of rodents scattered over large areas, the wearing of protective clothing is the most practical method of prophylaxis. CURATIVE TREATMENT was revolutionised by the introduction of CHLORAMPHENICOL and the TETRACYCLINES. These antibiotics altered the prognosis in typhus fever very considerably.... typhus fever
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