Rocky Mountain Spotted Fever

Organism Rickettsia rickettsii.

Clinical features The illness commences suddenly with onset of high fever, headache, malaise, muscle pains and rash. Appearing about the third day, the characteristic rash is maculo-papular from numerous petechial haemorrhages and covers the whole body including the palms and soles.

Diagnosis is made clinically with the additional help of enzyme immunoassay and immunofluorescence tests containing the specific antigen.

Transmission Humans are infected by the bite of a tick although infection can also be acquired by scratching in tick faeces or crushing the tick on the skin or mucous membranes. Larval and nymphal stages, as well as adult ticks, can transmit the infection. Rickettsial infection is maintained by transovarial transmission and the tick acts as the reservoir.

Incubation period 3-14 days.

Period of communicability Since the tick is the reservoir of infection, it is not spread from person to person.

Occurrence and distribution First described in the Rocky Mountains of North America, the disease is also found in Mexico, Panama, Costa Rica, Brazil, Colombia and Argentina.

Control and prevention Prevention is by avoiding any known tick country or wearing protective clothing, treated with repellents or insecticides. The common vector in North America is the dog tick, D. variabilis, or the wood tick D. andersoni so the control of dogs and their ectoparasites with tick-repellent collars is effective. Amblyomma cajennense is the main vector in the rest of the Americas.

Treatment is with doxycycline, tetracycline or chloramphenicol.

Surveillance Dogs and other animals should be checked regularly for ticks.

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