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an order of bacteria comprising small, gram-negative, rod-shaped or coccoid, often pleomorphic microorganisms occurring as elementary bodies that typically multiply only inside the cells of the host. Found as parasites in both vertebrates and invertebrates, which may serve as vectors, they may be pathogenic for both humans and other animals.
Rickettsiales/Rick·ett·si·a·les/ (rĭ-ket″se-a´lēz) an order of gram-negative bacteria occurring as elementary bodies that typically multiply only inside cells of the host. Parasitic for vertebrates and invertebrates, which serve as vectors, they may be pathogenic for humans and other animals.
an order of bacteria containing the families Rickettsiaceae and Anaplasmataceae. Small, obligately intracellular, gram-negative coccobacillary bacteria parasitizing host cells as a source of ATP. They are found in wild mammals, ticks, lice and trematodes and are transmitted by bites of arachnid or insect bites or by ingestion of trematodes. Generally replicate within erythrocytes, leukocytes or endothelial cells.