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Home Books Jawetz, Melnick, & Adelberg’s Medical Microbiology, 27e

Chapter 26: Rickettsia and Related Genera

GENERAL

The human pathogens in the family Rickettsiaceae are small bacteria of the genera Rickettsia and Orientia. They are closely related to members of the family Anaplasmataceae that includes the genera Ehrlichia and Anaplasma. These organisms are obligate intracellular parasites that are transmitted to humans by arthropods. Many rickettsiae are transmitted transovarially in the arthropod, which serves as both vector and reservoir. Rickettsial infections, but not the ehrlichioses, typically are manifested by fever, rashes, and vasculitis. They are grouped on the basis of their clinical features, epidemiologic aspects, and immunologic characteristics (Table 26-1). Coxiella burnetii resides in the family Coxiellaceae and is more closely related to the genus Legionella; for convenience, it is discussed at the end of this chapter.

TABLE 26-1Rickettsial, Ehrlichial Diseases, and Q Fever
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TABLE 26-1 Rickettsial, Ehrlichial Diseases, and Q Fever
Group Organism Disease Geographic Distribution Vector Mammalian Reservoir Clinical Features Diagnostic Testsa
Typhus group Rickettsia prowazekii Epidemic typhus (louse-borne typhus), Brill-Zinsser disease Worldwide: South America, Africa, Asia, North America Louse Humans Fever, chills, myalgia, headache, rash (no eschar); severe illness if untreated Serology
Rickettsia typhi Murine typhus, endemic typhus, flea-borne typhus Worldwide (small foci) Flea Rodents Fever, headache, myalgia, rash (no eschar); milder illness than epidemic typhus Serology
Scrub typhus group Orientia tsutsugamushi Scrub typhus Asia, South Pacific, northern Australia Mite Rodents Fever, headache, rash (50% have eschar), lymphadenopathy, atypical lymphocytes
Spotted fever groupb Rickettsia rickettsii Rocky Mountain spotted fever Western Hemisphere (United States, South America) Tickc Rodents, dogs Fever, headache, rash (no eschar); many systemic manifestations Direct FA of rickettsiae in tissue; serology; PCR
Rickettsia conorii Fièvre boutonneuse, Mediterranean spotted fever, Israeli spotted fever, South African tick fever, African (Kenya) tick typhus, Indian tick typhus Mediterranean countries, Africa, Middle East, India Tickc Rodents, dogs Fever, headache, rash, “tache noire” (eschar) Direct FA of rickettsiae in tissue not sensitive; serology
Rickettsia sibirica Siberian tick typhus (North Asian tick typhus) Siberia, Mongolia Tickc Rodents Fever, rash (eschar) Serology
Transitional group Rickettsia akari Rickettsial pox United States; Russia; Korea; South Africa Mitec Mice Mild illness, fever, headache, vesicular rash (eschar) Serology
Rickettsia australis Queensland tick typhus Australia Tickc Rodents, marsupials Fever, rash of trunk and limbs (eschar) Serology
Q fever Coxiella burnetii Q fever Worldwide Airborne fomites tick Sheep, cattle, goats, others Headache, fever, fatigue, pneumonia (no rash); can have major complications Positive CF to phase I, II antigens
Ehrlichiae Erlichia chaffeensis Human monocyte ehrlichiosis South-central, southeastern, and western United States Tick Deer, dogs, humans Fever, headache, atypical white blood cells Inclusions in circulating monocytes; indirect FA for antibodies
Anaplasma phagocytophilum Human granulocyte anaplasmosis Upper midwestern, northwestern, and West Coast United States and Europe Tick Mice, other mammals Fever, headache, myalgia Inclusions in granulocytes; indirect FA for antibodies
Ehrlichia ewingii Ewingii ehrlichiosis Midwestern United States Tick Dogs Fever, headache, myalgia Inclusions in granulocytes; indirect ...

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