Endemic typhus (murine typhus) is a flea‑borne rickettsial infection caused by Rickettsia typhi, an obligate intracellular, gram-negative bacteria transmitted from rodents to humans by flea bites or aerosolized flea feces. The rat flea (Xenopsylla cheopis) serves as the principal vector worldwide but, in the United States, the principal vector is the cat flea (Ctenocephalides felis). The mouse flea (Leptopsylla segnis) may also contribute to transmission.

Endemic typhus is found worldwide in areas with the primary reservoir (rats worldwide and opossums and cats in the United States) and the vector flea. It is a significant cause of febrile human disease in many tropical and subtropical areas. Seasonal incidence of human infections correlates with periods of abundance of vector fleas, usually summer months in the United States. A risk factor for infection is employment in a granary or brewery. Sanitation workers (garbage collectors) are at an especially high risk. Transmission occurs in domestic settings in the developing world.

In the United States, most cases occur in Texas (primarily South Texas, although new areas of endemicity have emerged), California (primarily areas of Los Angeles and Orange counties), and Hawaii (primarily Maui County, with sporadic cases on all other islands). Louisiana also detected an increase in flea-borne typhus cases in 2025 and 2026.

After the flea bite, there is a 7- to 14-day incubation period. Rapid onset of flu-like illness occurs (fever in almost all cases, chills, nausea, severe headache, and myalgias) and lasts about 2 weeks. A generalized macular, papular, and/or petechial eruption develops in 50% of cases. The rash can persist for up to 10 days or fade rapidly after 2-3 days.

In untreated cases, rickettsia-induced cerebral microvascular endothelial injury and vasculitis may result in encephalopathy, manifesting as confusion, delirium, stupor, apathy, meningismus, or coma. Patients may also develop renal, hepatic, cardiac, and pulmonary dysfunction; however, the disease is typically mild in most individuals. Rare severe complications include uveitis and septic shock with multiorgan failure. Overall, mortality remains low at approximately 1%-2% in untreated cases, predominantly affecting older adults, and many infections are subclinical with spontaneous resolution, even without therapy.