Rickettsial Disease

Descriptive text is not available for this imageBASICS

DESCRIPTION

  • Disorders caused by the Rickettsiae family of organisms including those that cause Rocky Mountain spotted fever (RMSF) and other similar tick-borne illnesses, the typhus group Neoehrlichia, Neorickettsia, 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.

EPIDEMIOLOGY

  • There are geographical differences in distribution of disease in the United States and worldwide.
  • Can occur year-round; annual incidence rates have been increasing.
  • In the United States, RMSF has the highest rates of severe disease with fatal outcomes; children <10 years of age have the highest case-fatality rate.

ETIOLOGY

  • Spotted fever group Rickettsia and the agents of neoehrlichiosis, ehrlichiosis and anaplasmosis (Ehrlichia and Anaplasma species), are transmitted to humans by ticks.
  • Rickettsialpox (Rickettsia akari) and scrub typhus (Orientia tsutsugamushi) are transmitted by mites associated with mice.
  • Epidemic typhus (Rickettsia prowazekii) is a louse-borne illness.
  • Endemic typhus, also known as murine typhus (Rickettsia typhi), is transmitted by fleas.
  • The rickettsial diseases that occur in the United States are spotted fever group rickettsioses, including RMSF (Rickettsia rickettsia), Rickettsia parkeri, Pacific Coast tick fever (Rickettsia species 364D), and rickettsialpox; murine typhus; epidemic typhus; ehrlichiosis; and anaplasmosis.

GENERAL PREVENTION

  • Fleas, ticks, lice, 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.

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