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Rocky Mountain spotted fever is caused by Rickettsia
rickettsii, a very small bacterium that must live inside the
cells of its hosts. These bacteria range in size from 0.2 x 0.5
micrometers to 0.3 x 2.0 micrometers. They are difficult to see in
tissues by using routine histologic stains and generally require the
use of special staining methods (Figure 5).
Figure 5. Gimenez stain of tick hemolymph cells
infected with R. rickettsii
In humans, rickettsiae live and multiply primarily within cells
that line small- to medium-sized blood vessels. Spotted fever group
rickettsiae can grow in the nucleus or in the cytoplasm of the host
cell. Once inside the host the rickettsiae multiply, resulting in
damage and death of these cells. This causes blood to leak through
tiny holes in vessel walls into adjacent tissues. This process
causes the rash that is traditionally associated with Rocky Mountain
spotted fever and causes damage to organs and tissues.
Taxonomy
The genus Rickettsia is included in the bacterial tribe
Rickettsieae, family Rickettsiaceae, and order
Rickettsiales. This genus includes many other species of
bacteria associated with human disease, including those in the
spotted fever group and in the typhus group. There are 18 species
currently recognized in the spotted fever group (Figure 6).
Figure 6. Taxonomic
classification of the order Rickettsiales
Other Pages with information on Rocky Mountain Spotted Fever:
Rocky
Mountain Spotted Fever - History
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Rocky Mountain Spotted Fever Overview
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Rocky
Mountain Spotted Fever The Organism
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Rocky Mountain Spotted Fever
Epidemiology
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Rocky Mountain Spotted Fever
Signs and Symptoms
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Rocky Mountain spotted fever
Detection
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Rocky Mountain Spotted Fever
Treatment
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Rocky Mountain Spotted Fever
Prevention and Control
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