any of a group of parasitic bacteria that live in arthropods (as ticks and mites) and can cause disease if transmitted to human beings

a microbe that is somewhere between a bacteria and a virus

disease causing microorganisms, smaller than bacteria but larger than viruses. Usually transmitted to humans by the bites of fleas, lice and ticks.

a group of small bacteria that live inside tissue cells, and are carried by ticks, mites, fleas or lice.

Any of a family (Rickettsiaceae) of pleomorphic rod-shaped nonfilterable microorganisms that cause various diseases (as typhus).

Rickettsia is a genus of non-motile, Gram-negative, non-sporeforming, highly pleomorphic bacteria that can present as cocci (0.1 μm in diameter), rods (1-4 μm long) or thread-like (10 μm long). Obligate intracellular parasites, the Rickettsia depend on entry, growth, and replication within the cytoplasm of eukaryotic host cells (typically endothelial cells). Because of this, Rickettsia cannot live in artificial nutrient environments and are grown either in tissue or embryo cultures (typically, chicken embryos are used).