Several different illnesses called "typhus" exist, all of them caused by one of the bacteria in the family Rickettsiae. Each illness occurs when the bacteria is passed to a human through contact with an infected insect.
The four main types of typhus are:
These diseases are all somewhat similar, although they vary in terms of severity. The specific type of Rickettsia that causes the disease also varies, as does the specific insect that can pass the bacteria along.
Epidemic typhus is caused by Rickettsia prowazekii, which is carried by body lice. When the lice feed on a human, they may simultaneously defecate. When the person scratches the bite, the feces (which carry the bacteria) are scratched into the wound. Body lice are common in areas in which people live in overcrowded, dirty conditions, with few opportunities to wash themselves or their clothing. Because of this fact, this form of typhus occurs simultaneously in large numbers of individuals living within the same community; that is, in epidemics. This type of typhus occurs when cold weather, poverty, war, and other disasters result in close living conditions that encourage the maintenance of a population of lice living among humans. Epidemic typhus is now found in the mountainous regions of Africa, South America, and Asia.
Brill-Zinsser disease is a reactivation of an earlier infection with epidemic typhus. It affects people years after they have completely recovered from epidemic typhus. When something causes a weakening of their immune system (like aging, surgery, illness), the bacteria can gain hold again, causing illness. This illness tends to be extremely mild.
Endemic typhus is carried by fleas. When a flea lands on a human, it may defecate as it feeds. When the person scratches the itchy spot where the flea was feeding, the bacteria-laden feces are scratched into the skin, thus causing infection. The causative bacteria is called Rickettsia typhi. Endemic typhus occurs most commonly in warm, coastal regions. In the United States, southern Texas and southern California have the largest number of cases.
Scrub typhus is caused by Rickettsia tsutsugamushi. This bacteria is carried by mites or chiggers. As the mites feed on humans, they deposit the bacteria. Scrub typhus occurs commonly in the southwest Pacific, southeast Asia, and Japan. It is a very common cause of illness in people living in or visiting these areas. It occurs more commonly during the wet season.
Causes and symptoms
The four types of typhus cause similar types of illnesses, though varying in severity.
Epidemic typhus causes fever, headache, weakness, and muscle aches. It also causes a rash composed of both spots and bumps. The rash starts on the back, chest, and abdomen, then spreads to the arms and legs. The worst types of complications involve swelling in the heart muscle or brain (encephalitis). Without treatment, this type of typhus can be fatal.
Brill-Zinsser disease is quite mild, resulting in about a week-long fever, and a light rash similar to that of the original illness.
Endemic typhus causes about 12 days of high fever, with chills and headache. A light rash may occur.
Scrub typhus causes a wide variety of effects. The main symptoms include fever, headache, muscle aches and pains, cough, abdominal pain, nausea and vomiting, and diarrhea. Some patients experience only these symptoms. Some patients develop a rash, which can be flat or bumpy. The individual spots eventually develop crusty black scabs. Other patients go on to develop a more serious disease, in which encephalitis, pneumonia, and swelling of the liver and spleen (hepatosplenomegaly) occur.
A number of tests exist that can determine the reactions of a patient's antibodies (immune cells in the blood) to the presence of certain viral and bacterial markers. When the antibodies react in a particular way, it suggests the presence of a rickettsial infection. Many tests require a fair amount of time for processing, so practitioners will frequently begin treatment without completing tests, simply on the basis of a patient's symptoms.
The prognosis depends on what types of complications an individual patient experiences. While children usually recover well from epidemic typhus, older adults
Walker, David, et al. "Rickettsial Diseases." In Harrison's Principles of Internal Medicine, ed. Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.
Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. <http://www.cdc.gov>.
Rosalyn Carson-DeWitt, MD
Antibody—Specialized cells of the immune system, which can recognize organisms that invade the body (such as bacteria, viruses, and fungi). The antibodies are then able to set off a complex chain of events designed to kill these foreign invaders.
Endemic—Occurring naturally and consistently in a particular area.
Epidemic—A large cluster of cases all occurring at about the same time within a specific community or region.