Rickettsial Disease

Basics

Disorders caused by the Rickettsiae family of organisms including those which cause Rocky Mountain spotted fever and other similar tick-borne illnesses, the typhus group, and the organisms that cause ehrlichiosis and anaplasmosis
All organisms are obligate intracellular gram-negative bacteria and therefore are difficult to grow in culture.
The diseases caused by each group of organisms are similar, encompassing a syndrome including fever, rash, headache, and capillary leak; all are transmitted via an insect vector.

Fleas, ticks, and mites should be controlled in endemic areas with the appropriate insecticides.
Clothing to cover the entire body should be worn in tick-infested areas. In the case of a recognized bite, ticks should be removed from human skin properly, with care not to expel the contents of the tick’s stomach into the site of the bite.
In areas where louse-borne typhus is epidemic, periodic delousing and dusting of insecticide into clothes are recommended.
Paradoxic effect of rodenticides:
- Fleas and mites seek alternate hosts (i.e., humans) when mice or rats are not present.
- Therefore, rodenticides should not be the only preventive measure taken in endemic areas.
Except for scrub typhus, all rickettsial diseases produce long-term immunity to the etiologic organisms within the same group.

Spotted fever, typhus, ehrlichiosis, and anaplasmosis groups cause vasculitis as a result of organisms invading the endothelial cells of small blood vessels or white blood cells.
This vasculitis manifests as rash in cutaneous tissues and systemic illness due to capillary leak throughout other organs.

Spotted fever group Rickettsia and the agents of ehrlichiosis and anaplasmosis (Ehrlichia and Anaplasma species) are transmitted to humans by ticks.
Rickettsialpox and scrub typhus are transmitted by mites associated with mice.
Epidemic typhus is a louse-borne illness, and endemic typhus, also known as murine typhus, is transmitted by fleas.
The rickettsial diseases that occur in the United States are Rocky Mountain spotted fever, murine typhus, rickettsialpox, epidemic typhus, ehrlichiosis, and anaplasmosis.

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