Rickettsia prowazeki (causes the disease epidemic typhus)

Life > Eubacteria > Phylum: Proteobacteria > Class: "Alphaproteobacteria" > Order: Rickettsiales > Family: Rickettsiaceae > Genus: Rickettsia

The bacterium that causes the disease  epidemic typhus, transmitted to humans by the Human Body Louse.

Rickettsia prowazeki causes epidemic typhus which kills people as a result of encephalitis (inflammation of the brain), myocarditis (inflammation of the heart muscle) or pneumonia (inflammation of the lungs).  The vector that transmits this disease organism to humans is the Human Body Louse Pediculus humanus. People become infected when faeces of an infected louse contaminate punctured skin or when a person breaths in airborne organisms from clothing with louse faeces. Lice can't live long off people so they spread most readily in overcrowded conditions. There were about 30 million infections and 3 million deaths from epidemic typhus in eastern Europe and Russia from 1918 to 1922. Through all of human history, it is claimed that more people have been killed by epidemic typhus than by all the wars combined. Epidemics are usually associated with conditions where there has been a complete breakdown in living conditions, often the result of war. A recent example is an outbreak of this disease in Burundi refugee camps that infected about 30000 people.

Like other Rickettsia species, R. prowazeki is an obligate intracellular parasite in both its mammalian and arthropod host. Lice infected with R. prowazekii, die about two weeks after sucking up the infected blood and the disease is not transmitted to their eggs (transovarial transmission). As a result, the mammalian host is essential in long term propagation of R. prowazeki. R. prowazeki can go into a phase where it exists in some people without affecting them and in this way is available for infection of lice that bite their human host. Flying Squirrels Glaucomys volans in the eastern United States have been found to be hosts of R. prowazeki in addition to people, and the parasite is also able to infect lice and flea parasites on the squirrels.

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Text by Hamish Robertson


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