Rickettsial Disease

Basics

Description

  • 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.

General Prevention

  • 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.

Pathophysiology

  • 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.

Etiology

  • 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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