WANTED: Rickettsia rickettsii

Beware, causes Rocky Mountain spotted fever

Spread By

R. rickettsii is spread by infected ticks. Humans are considered to be accidental hosts in the Rickettsia–tick life cycle and are not required to maintain the rickettsiae in nature.

Diseases caused by Rickettsia rickettsii

Brazilian spotted fever or São Paulo fever (Brazil), Tobia fever (Colombia), Fiebre manchada (Mexico), and Rocky Mountain Spotted Fever (United States).

Despite the name “Rocky Mountain Spotted Fever,” during recent decades cases have predominated in the southern Atlantic states (especially N. and S. Carolina) and lower Midwest (especially Missouri, Arkansas, and Oklahoma).

Disease symptoms

Classical triad includes fever, severe headache, and rash.

Rash is fully present up to 5 days after the onset of fever, though cases without rash can be observed in elderly or African-American patients, and usually associated with more severe cases, probably because of the late diagnosis in the absence of typical rash.

Cases per year, and when they happen

Between 1996 and 2000, the number of cases of RMSF reported in the US was between 400 and 600 cases per year. The number of recognized cases increased to over 1000 in 2002.

More than 90% of cases in the US are reported during April through September.

Background Information

First described in the Snake River Valley (Idaho) in 1896.

Classified (Category B) as bioterrorism agent by the CDC.

Endemic in the US and in several other parts of the Western hemisphere: Canada, Mexico, Costa Rica, Panama, Colombia, Brazil, and Argentina; in the US, Rickettsia rickettsii has become more common in the central southwest and south Atlantic states than in the Rocky Mountains.

In many parts of the world, it is considered as an emergent or re-emergent disease.

Carriers (Vectors and Reservoirs)

Though Ticks are well known to carry the disease, animals of all kinds can carry it too.
Other reservoirs include wild rodents, dogs, horses and donkeys.


Doxycycline and Chloramphenicol are the most common drugs of choice for reducing the symptoms associated with RMSF. When it is suspected that a patient may have RMSF, it is crucial that antibiotic therapy be administered promptly. Failure to receive antibiotic therapy, especially during the initial stages of the disease, may lead to end-organ failure (heart, kidney, lungs, meningitis, brain damage, shock, and even death.
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