Reported cases of Rocky Mountain spotted fever reached an all-time high in 2004. Scientists have now traced some cases occurring in eastern Arizona to a newly discovered vector: the brown dog tick common on domestic dogs. Previously, two less common types of tick were primarily associated with transmission of the disease, which is caused by Rickettsia rickettsii bacteria. Although infected dog ticks have been found only in Arizona so far, this type of tick is widespread.

Despite its name, Rocky Mountain spotted fever is found across the United States-over half of cases occur in the east. Although easily treated with doxycycline if diagnosed early, it's extremely dangerous if untreated.

All health care providers are urged to question patients with suspicious signs and symptoms about recent travel and tick bites. Initial signs and symptoms include fever, nausea, vomiting, muscle pain, lack of appetite, and severe headache. Late signs include a red spotted (petechial) rash, abdominal and joint pain, and diarrhea.

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