Rickettsia akari - Classification, Morphology, Clinical Manifestation, Culture

Classification of Rickettsia akari

Domain: Bacteria

Phylum: Pseudomonadota

Class: Alphaproteobacteria

Order: Rickettsiales

Family: Rickettsiaceae

Genus: Rickettsia

Species group: Spotted fever group

Species: akari

Clinical Manifestation of Rickettsia akari

Rickettsia akari is the causative agent of Rickettsial pox and is transmitted via mites.

The incubation period is 7 days. Symptoms include fever, myalgia, headache, and malaise. After 3-4 days of the appearance of fever, the generalized papular vesicular rash develops.

In 2-3 weeks, Rickettsia akari recovers with complete healing of the rash.

Morphology of Rickettsia akari

Morphologically, Rickettsia akari is gram-negative bacilli that are pleomorphic, obligate, intracellular, and fastidious with a size of 0.3 x 1-2 μm. It has a very small genome composed of 1-1.5 million bp. They multiply by binary fission within the cytoplasm of eukaryotic cells.

The bacteria are non-capsulated, non-motile, and contain a loose slime layer.

Rickettsia akari target cells in a host such as the reticuloendothelial system which releases mature rickettsiae resulting in the lysis of host cells. Rickettsiae are primary pathogens of arthropods (lice, fleas, ticks, mites) and are present in the intestinal tract- transmitted by arthropod vectors.

Rickettsia akari has LPS and peptidoglycan later. The LPS shows weak endotoxic activity. Moreover, they are poorly Gram-stained but stained well with Giemsa and Castaneda staining.

Culture of Rickettsia akari

Rickettsia akari fails to grow in cell-free media and grows in the cell line, chick embryo, and animal inoculation.

Cell lines such as HeLa, Hep 2, are used to maintain culture for primary isolation. Culture in yolk sack done for vaccine preparation. Animal inoculation is done in guinea pigs and mice. The optimum temperature 32-35°C,