The Causitive Agent of Rocky Mountain Spotted Fever Essay

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The Causitive Agent of Rocky Mountain Spotted Fever

The Bacteria

Rickettsia rickettsii is the small, aerobic gram-negative bacterium that is the cause Rocky Mountain spotted fever in humans (and other vertebrates). They are obligate, intracellular bacteria that range in size form 0.2x0.5 µm to 0.3x2.0µm. Rickettsia belong to the phylum alpha-protobacteria, which are capable of growing in low levels of nutrients, and have a long generation time relative to other gram negative bacteria such as Escherichia coli. In humans rickettsiae preferentially reside in the nucleus or cytoplasm of cells lining small to medium size blood vessels.

Rickettsia enter host cell by inducing phagocytosis, then immediately escape the phagosome to grow
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The bite of an infected tick is the primary mode of transmission to humans, or other vertebrate hosts, though it is also possible, but extremely rare for infection to result from exposure to crushed tick tissues, fluids, or feces. (http://www.cdc.gov/ncidod/dvrd/rmsf/Natural_Hx.htm)

The Disease

“RMSF is the most common fatal human tick-borne disease in the United States, with a minimal average of 351 confirmed human cases occurring annually and undoubtedly many more going unreported” (Niebylski et al.).

There are three major symptoms associated with RMSF which usually appear after an incubation period of five to ten days: fever, headache, and a rash. The rash is a diffuse macular (featuring elevated discoloration) rash, is most prominent on wrists and ankles, which will usually erupt three or four days after the onset of fever. All three of the primary symptoms are not always present in all cases of RMSF, making it much harder to correctly diagnose the disease. Other symptoms are general symptoms common with other types of infections such as vomiting, diarrhea, and abdominal pain. Despite the name the disease is endemic in the Carolinas, Oklahoma, and Tennessee, and is less common in the Rocky Mountain area. About 95% of reported cases occur between April and September. (Lyon and Kelsey).

Case fatality rate can be as high as 30% for untreated patients. With quick diagnosis and proper treatment fatalities are extremely rare. The most