rocky mountain spotted fever

Rocky mountain spotted fever is a potentially dangerous tick born disease caused by the organism Rickettsia rickettsii. It typically presents with a combination of fever, headache and rash in a tick-exposed individual. However, the classic "triad" occurs in about half of patients, and the diagnosis may be missed especially early on in the illness because of lack of specific symptoms or failure to consider the possibility.

It is transmitted in the eastern and southeastern US by the dog tick; in the Rocky Mountain area the vector is the wood tick (Lyme disease is generally spread by the deer tick). The tick does not have to bite to transmit the disease, so any history of tick exposure is significant for RMSF, even pulling a tick off the child's clothing. Most patients are 15 years old or younger, probably owing to their increased propensity for exhuberant romping through the underbrush and subsequent tick exposure.

There are about 600 cases per year in the US. North Carolina is the state with the highest incidence. RMSF typically occurs in the spring and summer, with most cases appearing from April to September; but the illness can occur in any month.

RMSF is a vasculitis - an inflammation of blood vessels caused by invasion of the lining cells of the blood vessels by the rickettsia organism. Clotting off (thrombosis) of microscopic blood vessels and inflammation of the capillary walls leads to leakage of blood around the break - hence, petechiae. The characteristic petechiae do not blanch when pressed in the way that simple inflammatory rashes do.

The incubation period is 2-12 days. RMSF is always a febrile illness. The patient may have the disease with no rash but never the disease with no fever. The rash is often lacking first three days of illness. It may start as more non-descript flat red spots but then progresses to classic petechiae. Classically, the rash involves the palms and soles (a "centripetal" rash) and spreads centrally to involve the arms, legs and eventually the trunk. The rash is totally absent in only about 5% of cases; these are natuarally the most difficult to diagnose. Other symptoms beside the classic severe headache include photophobia (light bothers the eyes intensely), as well as symptoms of abdominal pain, nausea, vomiting or diarrhea.

The treatment of choice is oral doxycycline for 5-7 days; it provides dramatic relief of symptoms and cessation of the fever. Doxycycline is a tetracycline type antibiotic. Earlier worries about staining of the permanent teeth from tetracycline use in children under the age of eight have proven to be groundless for the short 5 to 7 day course of therapy usually required. While the disease can be rapidly fatal if diagnosed too late, with early detection and prompt treatment, the cure is complete. For this reason, treatment is often given on suspicion of disease in high-risk areas of the country.

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