Rickettsia

Rickettsiae, or rickettsial bacteria, are primarily obligate intracellular parasites, meaning they cannot grow and reproduce outside the cells of the host. They are widely distributed in animal and human tissues, but due to the lack of suitable conditions (temperature, humidity, availability of food) they are in an inactive state.

The 160 species of Rickettsioidaedes are classified into three families: Rickettsiaceae (3 species), Ehrlichaliaceae (95), Anaplasmataceae (52). The largest family is Rickettsiaceae, when classifications are often used to further group subfamilies.