GENERAL CHARACTERISTICS OF RICKETTSIA

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GENERAL CHARACTERISTICS OF RICKETTSIA

Rickettsia is a genus of nonmotile, Gram negative, nonspore-forming, highly pleomorphic bacteria that may occur in the forms of cocci, bacilli, or threads.

 

GENERAL CHARACTERISTICS OF RICKETTSIA

Pleomorphic organisms are microorganisms who have the ability to alter their morphology, biological functions or reproductive modes in response to environmental conditions.

 

 

The term “rickettsia” has nothing to do with rickets (which is a deficiency disease resulting from lack of vitamin D): the bacterial genus Rickettsia was named after Howard Taylor Ricketts, in honor of his pioneering work on tick-borne spotted fever.

 

The rickettsiae are a diverse collection of obligately intracellular Gram-negative bacteria found in ticks, lice, fleas, mites, chiggers, and mammals. These zoonotic pathogens cause infections that disseminate in the blood to many organs.

 

 

Clinical Manifestations of Rickettsia

Rickettsia species cause Rocky Mountain spotted fever, rickettsial pox, other spotted fevers, epidemic typhus, and murine typhus. Orientia (formerly Rickettsia) tsutsugamushi causes scrub typhus. Patients present with febrile exanthems and visceral involvement; symptoms may include nausea, vomiting, abdominal pain, encephalitis, hypotension, acute renal failure, and respiratory distress.

 

 

Structure, Classification, and Antigenic Types of Rickettsia

Rickettsia species are small, Gram-negative bacilli that are obligate intracellular parasites of eukaryotic cells. This genus consists of two antigenically defined groups: spotted fever group and typhus grow.

 

 

PATHOGENESIS OF RICKETTSIA

Rickettsia are transmitted by the bite of infected ticks or mites or by the feces of infected lice or fleas. From the portal of entry in the skin, rickettsiae spread via the bloodstream to infect the endothelium and sometimes the vascular smooth muscle cells. Rickettsia species enter their target cells, multiply by binary fission in the cytosol, and damage heavily parasitized cells directly.

 

 

 

CONTROL OF RICKETTSIA

Rickettsia species are susceptible to the broad-spectrum antibiotics, doxycycline, tetracycline, and chloramphenicol. Prevention of exposure to infected arthropods offers some protection. A Vaccine exists for epidemic typhus but is not readily available.

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