: any of a family (Rickettsiaceae) of rod-shaped, coccoid, or diplococcus-shaped, often pleomorphic gram-negative bacteria that are intracellular parasites of arthropods (as lice or ticks) and when transmitted to humans cause various diseases (as typhus)
New Latin, genus name, from Howard T. Ricketts †1910 American pathologist
First Known Use: 1919
Medical Definition of RICKETTSIA
capitalized: the type genus of the family Rickettsiaceae comprising rod-shaped, coccoid, or diplococcus-shaped often pleomorphic bacteria that live intracellularly in biting arthropods (as lice or ticks) and when transmitted to humans by the bite of an arthropod host cause a number of serious diseases (as Rocky Mountain spotted fever and typhus)
pluralrick·ett·si·ae\-ˌē\alsorick·ett·siasorrick·ett·sia: any bacterium of the order Rickettsiales and especially of the family Rickettsiaceae
Any of the rod-shaped bacteria that make up the family Rickettsiaceae (named for Howard Ricketts). They are rod-shaped or variably spherical, and most are gram-negative (seegram stain). Natural parasites of certain arthropods, they can cause serious diseases in humans and other animals, to which they are usually transmitted by a bite from an arthropod carrier. Because certain species can survive considerable drying, rickettsias can also be transmitted when arthropod feces are inhaled or enter the skin through abrasion. Typhus, trench fever, and Rocky Mountain spotted fever are rickettsial infections. The most effective treatment includes timely and prolonged administration of broad-spectrum antibiotics.