Rickettsial diseases

Abstract

<h2>Abstract</h2> Rickettsial diseases are transmitted by arthropod vectors and are responsible for various spotted and typhus fevers. Epidemic typhus fever (Rickettsia prowazekii) occurs in prisons, in refugee camps and during wars, when lice thrive in unhygienic, overcrowded conditions. Endemic typhus (R. typhi) arises when humans live close to flea-infested rodents, typically near granaries, breweries, shops and garbage tips. Spotted fever infections are contracted by humans in the rural habitat of the tick or mite vector and include Rocky Mountain (R. rickettsiae), Scrub typhus (Orientia tsutsugamushi), Mediterranean (R. conorrii) and African tick-bite (R. africae) fever. Spotted fevers are characterized by an eschar (black scab) at the site of the arthropod bite. A petechial or purpuric skin rash accompanies typhus and spotted fevers, though 10% of Rocky Mountain spotted fever and almost all cases of African tick-bite fever are ‘spotless'. Other features are headache, night sweats, lymphadenopathy and conjunctivitis. Vasculitic complications include gangrenous extremities, bowel perforation, liver dysfunction, renal failure, meningoencephalitis, disseminated intravascular coagulation and pneumonia. Laboratory diagnosis is by demonstration of seroconversion on paired samples using immunofluorescence assay. Tetracyclines are the mainstay of treatment. Children, pregnant women and those allergic to tetracyclines can be treated with chloramphenicol or newer macrolides. There are currently no vaccines against rickettsial diseases. Avoidance of the insect vector using protective clothing and topical repellents is recommended. Mortality may approach 10–25% in epidemic typhus and scrub typhus, but is lower (2–5%) in Mediterranean spotted fever and murine typhus.