Murine typhus, also known as endemic typhus, is an acute, febrile illness caused by the bacterium Rickettsia typhi. While it can cause severe symptoms, murine typhus is typically much milder than epidemic typhus, which is caused by a related but different bacterium. The disease is generally rare in developed areas, though its incidence has been rising in parts of the United States. The illness is not transmitted from person to person but occurs through an environmental cycle involving animals and insects.
The Cause and Spread of Murine Typhus
The specific pathogen responsible for this disease is the obligate intracellular bacterium Rickettsia typhi. The disease cycle traditionally involves rodents, primarily rats (Rattus species), which serve as the main reservoir for the bacteria. The infection is carried from the rodent to humans by an arthropod vector, most commonly the Oriental rat flea, Xenopsylla cheopis.
In certain areas of the United States, an alternate transmission cycle involves opossums and domestic or feral cats as reservoirs. In this suburban cycle, the cat flea, Ctenocephalides felis, acts as the primary vector responsible for spreading R. typhi to humans. People become infected when an infected flea feeds on a host and excretes bacteria-laden feces near the bite site.
The infection is not typically transmitted directly by the flea bite itself, but rather when the flea feces are rubbed or scratched into broken skin or mucous membranes. This can happen when a person scratches the irritated flea bite area, inadvertently introducing the bacteria into the bloodstream. In rare instances, inhaling dried, contaminated flea feces can also lead to infection.
Recognizing the Illness
After exposure, the incubation period usually ranges between 6 and 14 days. The onset of the illness is often sudden, with initial signs that can resemble a severe flu, making early diagnosis challenging. The classic presentation of murine typhus includes a triad of symptoms: a sustained high fever, an intense headache, and a rash.
The fever, which can be accompanied by chills and body aches, may persist for up to two weeks if the illness is not treated. The characteristic rash typically appears about five days into the illness and occurs in approximately 50 to 70 percent of patients. This rash is usually maculopapular, consisting of flat, red spots and small raised bumps.
The rash often begins on the trunk before spreading outward to the extremities. A distinguishing feature is that the rash usually spares the palms of the hands and the soles of the feet. Other common symptoms include nausea, vomiting, and abdominal pain, reflecting the systemic nature of the infection.
Diagnosis and Medical Management
Diagnosis begins with a high degree of clinical suspicion, based on a patient’s symptoms and a history of possible exposure to fleas or rodents. Because the symptoms are vague early on and overlap with many other infectious diseases, treatment should not be delayed while waiting for laboratory confirmation.
Laboratory confirmation typically relies on serologic testing, which detects antibodies the body produces against R. typhi. The most common method is the Indirect Immunofluorescence Assay (IFA), where a diagnosis is confirmed by demonstrating a four-fold or greater rise in antibody titer between an acute-phase blood sample and a convalescent-phase sample taken two to four weeks later. Detecting antibodies can be difficult in the first week of illness as the immune response has not fully developed.
Doxycycline is the standard antibiotic treatment for murine typhus and is the drug of choice for patients of all ages, including children. Treatment is most effective when initiated early and is typically continued until the patient has been without a fever for at least 48 hours. Timely antibiotic intervention significantly shortens the duration of the illness and helps prevent severe complications, such as involvement of the central nervous system or vital organs.
Prevention and Geographic Presence
Murine typhus occurs globally, particularly in warm, temperate, and subtropical climates. In the United States, the majority of cases are reported from specific warm-weather regions, most notably in southern California, southern Texas, and Hawaii. Cases tend to peak during the warmer months, from spring through early fall, when flea and rodent populations are most active.
Preventing the illness centers on reducing exposure to infected fleas and their animal hosts. This involves diligent rodent control around homes and communities, such as sealing any entry points and eliminating outdoor food sources that could attract rats or opossums. Flea control is also important, which includes regularly treating domestic pets with veterinarian-approved flea prevention products.
Since the infection is transmitted by flea feces, careful hygiene, such as avoiding contact with flea-infested areas and promptly cleaning up any animal droppings, is beneficial. There is no commercially available vaccine to protect humans against murine typhus. Therefore, environmental control measures remain the only effective strategy for avoiding this flea-borne illness.