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Medical Term:


Pronunciation: ri-ket'se-a


A genus of bacteria (order Rickettsiales) containing small (nonfilterable), often pleomorphic, coccoid to rod-shaped, gram-negative organisms that usually occur intracytoplasmically in lice, fleas, ticks, and mites but do not grow in cell-free media; pathogenic species infect humans and other animals, causing epidemic, murine, or endemic typhus, Rocky Mountain spotted fever, tsutsugamushi disease, rickettsialpox, and other diseases; type species is Rickettsia prowazekii.

[Howard T. Ricketts]

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