Typhus is a group of illnesses that share some commonalities. They are caused by species in the bacterial tribe Rickettsiae. The two typhus fevers are louse-borne typhus fever and murine typhus fever. Although they are caused by different bacteria, these illnesses are clinically similar and share the hallmark symptoms of high fever and a distinctive rash. Clinically, murine typhus fever is a milder version of louse-borne typhus fever. Scrub typhus is closely related to the typhus fevers, although it is a different illness.
Louse-Borne Typhus Fever
Louse-borne typhus fever is caused by the bacterium Rickettsia prowazekii, which is transmitted by the human body louse. Louse-borne typhus fever is also known as classic typhus or epidemic typhus because outbreaks occur in squalid conditions wherein people rarely bathe or change clothes. Throughout history, outbreaks of typhus have occurred during times of war and natural disasters.
Typhus bacteria infect the cells lining the blood vessels throughout the body. Approximately seven days after an infectious louse bite, the illness begins with high fever, chills, muscle aches and severe headache. The fever is quite high at 105 F to 106 F and persistent. On day four to six of the illness, a rash appears on the upper body and quickly spreads; only the palms, soles and face are unaffected. Serious complications include low blood pressure, severe dehydration, shock, kidney failure, encephalitis (brain inflammation), gangrene and pneumonia. The illness runs its course in approximately 14 days; the fever breaks and a protracted recovery begins. The disease may reactivate many years after the initial illness causing a milder version of classic typhus. The reactivation illness is called Brill-Zinsser disease.
Murine Typhus Fever
Murine typhus fever is caused by the bacterium Rickettsia typhi; the disease is transmitted to humans by rat fleas. The word murine refers to the scientific name of the animal group that includes rats and mice. Murine typhus occurs worldwide at a relatively constant level in any given location. This feature is why the illness is also known as endemic typhus.
Murine typhus is a milder illness than classic typhus. One to two weeks after the initial bite, the illness comes on abruptly with fever (103 F to 104 F) as the most common symptom. Other symptoms include severe headache, chills, muscle aches, nausea and vomiting. Notably, over the course of the illness, only 50 percent of patients develop a characteristic typhus rash. When the rash does occur, it is typically less severe than that seen with classic typhus. Neurologic symptoms such as confusion, stupor or seizures may occur in a minority of people with the illness. Left untreated, the fever usually breaks around day 12 of the illness and recovery follows.
Scrub Typhus
Scrub typhus is closely related to the typhus fevers, but it is a different illness. It is caused by the bacterium Orientia tsutsugamushi, which is in a different genus than the two bacteria that cause the typhus fevers. Humans contract scrub typhus from infected chiggers--the larval stage of rodent mites.
The clinical illness typically begins 10 to 12 days after the chigger bite. Symptoms include fever, chills, redness of the inner eyelids, cough, severe headache and swollen lymph nodes. The fever builds over the first several days of the illness reaching 104 F to 105 F. A rash appears on the trunk on day five to eight of the illness, which typically spreads to the arms and legs. Complications include severe dehydration, low blood pressure, altered level of consciousness and heart inflammation. Left untreated, the fever usually begins to break slowly after approximately 14 days.
References
- Centers for Disease Control and Prevention Yellow Book: Rickettsial and Related Infections
- Merck Manual: Epidemic Typhus
- Merck Manual: Murine (Endemic) Typhus
- Merck Manual: Scrub Typhus
- "Principles and Practice of Infectious Diseases, Sixth Edition"; Gerald L. Mandell, M.D., John E. Bennett, M.D., Raphael Dolin, M.D., Editors; 2004
