Treatment of Tropical and Travel Related Rickettsioses

Abstract

Infections with organisms of the genera Rickettsia and Orientia are undifferentiated in regard to their manifesting signs and symptoms. Hence, a high degree of suspicion is required when a patient has a compatible illness coupled with exposure to potential vectors. Confirmatory diagnosis is usually retrospective, as it is obtained through serologic methods to determine seroconversion or a fourfold increase in antibody titers from acute to convalescent phase sera. Since many of these infections are associated with considerable morbidity and mortality, empiric treatment is imperative when illness is suspected. Antibiotics in the tetracycline class are highly active in vitro and have an excellent track record in the treatment of these diseases. Of the antibiotics in this class, doxycycline is the drug of choice, as it has excellent bioavailability, ease of twice daily dosing, and more favorable gastrointestinal tolerability. The usual duration of treatment is 7 days. In the most severe rickettsiosis, Rocky Mountain spotted fever, use of the usual alternative, chloramphenicol, is associated with a higher case fatality rate. Therefore, doxycycline is recommended in children <8 years of age—short courses do not cause appreciable staining of developing permanent teeth. Chloramphenicol is not available in its oral form in the USA, and the parenteral formulation is becoming difficult to acquire. In countries where available, it should be used with careful consideration of the risk-benefit ratio when weighed against the pathogenicity of the suspected agent. For infection with less pathogenic spotted fever group and typhus group rickettsiae (e.g., R. conorii and R. typhi), fluoroquinolones are an alternative. The agent that causes scrub typhus, Orientia tsutsugamushi, is intrinsically resistant to fluoroquinolones. Azithromycin can be used for scrub typhus in areas where there is reported failure of doxycycline or when a safer agent is required (i.e., pregnancy).