rickettsioses

Rickettsioses are vector-borne diseases caused by obligate intracellular bacteria of the order Rickettsiales, mainly the genera Rickettsia and Orientia. They are transmitted to humans by arthropod vectors—ticks (spotted fever group), lice and fleas (typhus group), and mites (scrub typhus). Clinically they usually begin with fever, headache, myalgia, and often a rash; a possible eschar may be present at the bite site.

The main clinical groups are the spotted fever group (eg, Rickettsia rickettsii), the typhus group (R. prowazekii, R. typhi), and scrub typhus (Orientia tsutsugamushi). Severity ranges from mild to severe; complications include vasculitis with pneumonia, central nervous system involvement, and renal impairment.

Diagnosis relies on clinical suspicion plus laboratory testing. Serology by immunofluorescent assay (IFA) or enzyme-linked immunosorbent assay (ELISA) is standard; PCR can detect bacterial DNA early. The Weil-Felix test is rarely used today. A rise in antibody titer between acute and convalescent sera supports the diagnosis.

Treatment is typically doxycycline, started promptly; most patients defervesce within 2–3 days. Alternatives include chloramphenicol or macrolides (eg, azithromycin) in pregnancy or when doxycycline is unsuitable.

Prevention focuses on vector avoidance: protective clothing, insect repellents, tick checks, and prompt removal of ectoparasites. No widely available vaccines exist. Public health measures and vector-control programs reduce risk in endemic areas.