Murine typhus (also called epidemic or flea-borne typhus) is caused by Rickettsia prowazekii and spread from person to person by body lice containing the bacteria. It is often associated with overcrowded conditions that promote louse infestation and poor hygiene.
It is found worldwide but is most common in tropical and subtropical climates, especially in areas with high populations of rat-infested urban communities. It can also occur where people live with opossums and free-roaming cats that may carry the bacteria.
Causes
Typhus is caused by the bacterium Rickettsia rickettsii and transmitted to humans by fleas, ticks, mites, and lice. A human becomes infected with these bacteria when the parasite bites and contaminates its host with bacteria-laden saliva. Infection with the rickettsiae causes an acute febrile illness. Three different endemic typhus types occur in the United States: murine typhus, epidemic typhus, and scrub typhus.
People get a flea-borne form of typhus (epidemic or louse-borne typhus) when they are bitten by infected fleas and then scratch the bite wounds, which introduce the rickettsial organism into the skin. The bacterial infection spreads to other parts of the body from these scratched areas. People may also become infected by inhaling rickettsiae-contaminated dried flea feces. Some patients develop a relapsing form of typhus, called Brill-Zinsser disease, when latent rickettsial organisms reactivate in the body.
Endemic typhus is common in poor, unsanitary, crowded areas. The overall death rate from typhus is low for those who receive prompt treatment, but the rate is high for those who don’t seek medical attention or cannot afford quick treatments. The rash of typhus can resemble a variety of other conditions and may be difficult to distinguish from a measles, rubella, or Rocky Mountain spotted fever rash.
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The main cause of endemic typhus is the presence of a large population of body lice in crowded living conditions. These insects thrive in warm, humid, overcrowded areas and can multiply rapidly in a confined space. Those who live in such conditions are at increased risk of developing body lice and thus typhus infection, especially the young, old, or disabled.
In the United States, a majority of endemic typhus cases are due to murine typhus, which is carried by rat fleas (Xenopsylla cheopis). These fleas usually infest rats and other rodents but may also infest domestic cats, opossums, and house mice. Occasionally, this type of typhus is transmitted to humans by these animals, but more often it’s spread by infected human body lice or chiggers during their larval stages as scrub mites.
Symptoms
Murine typhus is caused by Rickettsia typhi and spread by fleas or lice that infest rat populations (epidemic typhus). It is common in the southern United States, particularly in California and Texas. It is also found in rural areas of Asia, Australia and Papua New Guinea. It’s sometimes called “Ebola fever” because it spreads like ebola virus when a louse, flea or tick infects a person with the bacteria then transfers them to other people (zoonotic typhus).
A rash develops in about one to two weeks after exposure. It’s usually a light rose color and fades when you press on it. The rash is accompanied by a high fever, headache, chills and fatigue. Other symptoms include a sore throat, malaise, nausea and vomiting and gastrointestinal upset. Some people develop a throbbing headache or muscle pain. A rash may appear on the hands and feet or all over the body. A scab, or eschar, forms at the site of the rash.
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The symptom pattern of scrub typhus resembles rheumatic fever. Often, people don’t remember being bitten by fleas, but they may have a history of traveling to an area where typhus is endemic. They may also have a history of contact with rat-infested environments, or they may have had a close encounter with a feral rat. The disease is transmitted by the bites of larval trombiculid mites (Xenopsylla cheopis and Ctenocephalides felis). Transmission to humans also occurs when a rat flea infects someone with its rickettsiae-laden feces, or when the person scratching the itchy bite spreads the bacteria around his or her open wounds by rubbing or scratching the skin.
In people with epidemic typhus, a sudden onset of fever, headache, chills and fatigue is followed by a rash that spreads to the chest, arms and legs. It can become very painful and disfiguring. A complication of typhus is anemia, caused by the loss of red blood cells from the body’s immune system fighting the infection. In severe cases, untreated typhus can lead to multiorgan failure, including kidney and heart failure. Prompt antibiotic treatment cures almost everyone with epidemic typhus.
Diagnosis
The diagnosis of typhus is made by examining the patient’s symptoms and performing laboratory tests. Because the incubation period is only about 1 to 2 weeks, most cases of typhus are diagnosed within two days of the onset of illness. The classic triad of fever, headache and skin rash is observed in about 15% of patients. In addition, many patients with endemic typhus have nonspecific symptoms such as chills, malaise, myalgias, arthralgias and nausea/vomiting. In addition, 40 to 50% of patients with endemic typhus develop a maculopapular rash that is usually discrete but can be more generalized and sometimes purpuric. The rash does not involve the palms or soles, unlike the rash caused by R. rickettsii, which does affect the hands and feet.
The bacteria that cause typhus, Rickettsia prowazekii and R. typhi, adhere to endothelial cells by their surface proteins. This allows the bacteria to enter through the bloodstream and spread throughout the body. Symptoms of typhus include a high fever, headache, chills and a skin rash (see the image below). A more severe form of the disease, scrub typhus, can cause complications including MODS (acute respiratory distress syndrome, encephalitis, liver failure or kidney failure), vascular shock and death.
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Murine typhus is the more common variety of this infection. It is spread by body lice that are infected with R. prowazekii and is typically associated with extremely crowded living conditions. It has also been reported in rural areas of California and in southern Texas. This type of typhus is not uncommon in children who live in rat-infested housing. It has also been associated with infected opossums and cat fleas.
The most reliable diagnostic tool for typhus is serology. Recovery of rickettsial antigens or antibodies from biological specimens is laborious and time-consuming, and a diagnosis may be delayed while the results are pending. Because of this, doctors often start antibiotic treatment before the lab test reports are available and may continue the medication until the results are confirmed or the illness resolves. Doxycycline, a tetracycline, is the drug of choice to treat all three types of typhus. However, a shorter course of the medication is preferred for pediatric patients because it can lead to tooth staining.
Treatment
In areas with endemic typhus, health care providers treat people who develop fever and signs and symptoms of the disease. The healthcare provider will order a blood test to look for antibodies to the bacteria that cause the infection. The bacterial DNA can also be tested using polymerase chain reaction techniques. PCR testing is more sensitive and specific than antibody testing. The eschar may also be cultured to look for the bacterium.
The bacterium Rickettsia prowazekii causes epidemic typhus. It is spread from person to person by the body louse (Pediculus humanus humanus). The louse becomes infected when it sucks a bite with its specialized mouthparts, releasing rickettsiae into the bloodstream. The bacteria invade the louse cells and multiply. The rickettsiae are then excreted by the louse into its feces. The infected louse can then transfer the rickettsiae to another person during repeated sucking, or by touching the contaminated feces with the unwashed hands of a person who has just been touched by the louse. The disease also can spread through a person breathing in the dried feces of an infected louse.
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Scrub typhus is caused by the bacterium Orientia tsutsugamushi, which is carried by mites that live on rodents and is transmitted through their bites. This type of typhus is found in Asia, Australia, Papua New Guinea and the Pacific Islands.
Symptoms of scrub typhus include fever, chills, headache, fatigue and a distinctive scab-like rash. People who get scrub typhus are more likely to have complications such as heart failure, pulmonary embolism and kidney failure, which can be fatal.
The treatment for typhus is antibiotics. The antibiotic doxycycline is effective in treating epidemic typhus, especially when given early in the course of illness. Other antibiotics such as ciprofloxacin may be used if doxycycline is not available or if the patient is allergic to it. Prevention of typhus includes basic hygiene such as frequent bathing, washing clothes on a regular basis and keeping away from wild animals that might carry lice or fleas. In addition, people who live in endemic typhus regions should wear insect repellent and avoid rat and flea bites.
