Rickettsial fever...... INFECTIOUS AGENT Rickettsial infections are caused by a variety of obligate intracellular, gram-negative bacteria from the genera Rickettsia, Orientia, Ehrlichia, Neorickettsia, Neoehrlichia, and Anaplasma, belonging to the Alphaproteobacteria Rickettsia were classically divided into the typhus group and spotted fever group (SFG), although the genus has been subdivided further based on phylogenetic analysis. Orientia spp. make up the scrub typhus group. TRANSMISSION Most rickettsial pathogens are transmitted by ectoparasites such as fleas, lice, mites, and ticks during feeding or by scratching crushed arthropods or infectious feces into the skin. Inhaling dust or inoculating conjunctiva with infectious material may also cause infection. The specific vectors that transmit each form of rickettsiae are Transmission of some rickettsial diseases after transfusion or organ transplantation is rare but has been reported. CLINICAL PRESENTATION Rickettsioses are difficult to specifically diagnose, even by physicians experienced with these diseases. Clinical presentations vary with the causative agent and patient; however, common symptoms that typically develop within 1–2 weeks of infection include fever, headache, malaise, and sometimes nausea and vomiting. Most symptoms associated with acute rickettsial infections are nonspecific. Many rickettsioses are accompanied by a maculopapular, vesicular, or petechial rash or an eschar at the site of the tick bite. African tick-bite fever should be suspected in a patient who presents with fever, headache, myalgia, and an eschar (tache noir) after recent travel to southern Africa. Mediterranean spotted fever should be suspected in patients with rash and fever after recent travel to northern Africa or the Mediterranean littoral. Scrub typhus should be suspected in patients with a fever, headache, and myalgia after recent travel to Asia; eschar, lymphadenopathy, cough, hearing difficulties, and encephalitis may also be present. Patients with typhus usually present with a severe but nonspecific febrile illness. Ehrlichiosis and anaplasmosis should be suspected in febrile patients with leukopenia and transaminitis with an exposure history. Most symptomatic rickettsial diseases cause moderate illness, but epidemic typhus and Rocky Mountain spotted fever can be severe and may be fatal in 20%–60% of untreated cases. DIAGNOSIS Diagnosis is usually based on clinical recognition and serology; the latter requires comparison of acute- to convalescent-phase serology, so is only helpful in retrospect. Etiologic agents can generally only be identified to the genus level by serologic testing. PCR and immunohistochemical analyses may also be helpful. If ehrlichiosis or anaplasmosis is suspected, a buffy coat may be examined to identify characteristic intraleukocytic morulae. .TREATMENT Treatment of patients with possible rickettsioses should be started early and should not await confirmatory testing. Treatment usually involves doxycycline. Chloramphenicol, azithromycin, fluoroquinolones, and rifampin may be alternatives, depending on the scenario. Expert advice should be sought if these alternative agents are being considered. PREVENTION No vaccine is available for preventing rickettsial infections. Antibiotics are not recommended for prophylaxis of rickettsial diseases.
Posted on: Sat, 27 Sep 2014 15:55:06 +0000
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