endemic typhus

Endemic typhus, also called murine typhus, is caused by Rickettsia typhi, an obligate intracellular gram-negative bacterium. The reservoir is rats (and sometimes cats/opossums), with transmission to humans via flea feces (Xenopsylla cheopis, the rat flea) that are inoculated into the skin through scratching—not via the bite itself. Pathophysiology involves rickettsial invasion of vascular endothelial cells, causing vasculitis, which underlies the clinical manifestations of fever, headache, myalgias, and a maculopapular rash that typically begins on the trunk and spreads centrifugally (sparing palms and soles in most cases, though this can vary). Compared to epidemic typhus (Rickettsia prowazekii, transmitted by body lice and associated with crowded/unsanitary conditions such as war or refugee camps), endemic typhus is generally milder, with lower rates of severe complications and mortality. However, if untreated, it can still cause significant morbidity, including rare complications such as pneumonitis, meningoencephalitis, and renal or hepatic dysfunction. Diagnosis is primarily clinical and epidemiologic (exposure to rats/fleas in endemic areas like the Gulf Coast, Southeast Asia, or other warm coastal regions), supported by serology (indirect immunofluorescence assay) since cultures are difficult and dangerous. Doxycycline is the treatment of choice, even in children, due to the risk of severe disease if untreated outweighing concerns about tetracycline-related tooth staining. On Step 1/Step 2, key distinguishing points to test include: vector (flea vs. louse), reservoir (rat vs. human), organism (R. typhi vs. R. prowazekii), and relative severity (endemic typhus milder than epidemic typhus, which can reactivate years later as Brill-Zinsser disease).