Rickettsia rickettsii

Rickettsia rickettsi is a rod-shaped immobile bacterium 1 × 0.3 μm in size, gram-negative , stained blue according to Romanowski-Giemsa . The shape of the cells may vary depending on the conditions and growth phase. It does not form endospores . R. rickettsii has a microcapsule and mucous membrane on the surface of the cell wall membrane . The latter consists of lipopolysaccharides , murein , protein antigens . The nucleoid is represented by a ring chromosome .

Rickettsia rickettsii , like viruses , is an obligate intracellular parasite . This bacterium has two hosts - ticks are intermediate, the main ones are mammals, including humans. Among ticks, the parasite is transmitted from one developmental phase to another and from generation to generation. Once in the bloodstream as a result of a tick bite, rickettsia primarily infects endothelial cells. Penetration into the cell occurs as follows: rickettsia attaches to the membrane and is phagocytized by the cell. Once inside, it is released from the phagosome and moves with the help of a flagellum . Leaving the cell, R. rickettsii does not destroy it.

Rickettsia rickettsii is transmitted by two types of ticks : Dermacentor andersoni and Dermacentor variabilis . Symptoms appear 3-12 days after being bitten by an infected tick. These include fever , severe headache , sudden chills . Almost always on the 2nd – 6th day of a fever, a rash appears - spotted pink rashes on the hands, in the ankle joints , palms, soles and forearms. Mortality is 7%.

Sensitive to most broad-spectrum antibiotics , especially the tetracycline series. For treatment, tetracycline , chloramphenicol is used .

Rickettsia do not grow on artificial nutrient media. In the laboratory, they are cultivated on chicken embryos or in tissue cultures.

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