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Epidemic typhus

From Academic Kids

Rickettsia prowazekii
Image:Rickettsia_prowazekii.jpg
Scientific classification
Kingdom:Bacteria
Phylum:Proteobacteria
Class:Alpha Proteobacteria
Order:Rickettsiales
Family:Rickettsiaceae
Genus:Rickettsia
Species:R. prowazekii
Binomial name
Rickettsia prowazekii

Epidemic typhus is a form of typhus caused by the bacillus Rickettsia prowazekii, carried by the human body louse Pediculus humanus. Feeding on a human who carries the bacillus infects the louse. R. prowazekii grows in the louse's gut and is excreted in the feces. The disease is transmitted to an uninfected human who scratches the bite and rubs the feces into the wound. Incubation period is one to two weeks. R. prowazekii can remain viable and virulent in the dried feces for many days. The disease will kill the louse and it will remain viable for many weeks in the dead louse.

Brill-Zinsser disease is a type of epidemic typhus which recurs in someone after a long period of latency (similar to the relationship between chickenpox and shingles). This type of recurrence can also occur in immunosuppressed patients.

Before World War II, epidemic typhus was a devastating disease for humans. Epidemics occurred throughout Europe from the 17th to the 19th centuries. It was common in prisons, where it was known as Gaol Fever. Before then there is little historical literature available. Widespread epidemics occurred during the Napoleonic Wars and the Irish potato famine of 1846 to 1849. During World War I the disease caused three million deaths in Russia and more in Poland and Romania. Even larger epidemics in the post-war chaos of Europe were only averted by the widespread use of the newly discovered DDT to kill the lice on millions of refugees and displaced persons. A vaccine was also developed in World War II, and today epidemics only occur in Eastern Europe, the Middle East and parts of Africa where living conditions and hygiene are poor.

According to Waclaw Szybalski [1] (http://www.lwow.home.pl/Weigl.html), the first description of typhus was given in 1083 in a convent near Salerno, Italy. In 1546, Girolamo Fracastoro, a Florentine physician, gave another description of typhus in his famous treatise on viruses and contagion, "De Contagione et Contagiosis Morbis."

Development of the Vaccine

Missing image
Epidemic_typhus_Burundi.jpg
Epidemic typhus rash

The first major step in the development of the vaccine was Charles Nicolle's 1909 discovery that lice were the vectors for epidemic typhus. This made it possible to isolate the bacteria causing the disease and develop a vaccine. Nicolle attempted a vaccine but was not successful in making one that worked on a large enough scale. He won the 1928 Nobel Prize for this work.

Henrique da Rocha Lima in 1916 then proved that the bacteria Rickettsia prowazekii was the agent responsible for typhus; he named bacteria after H. T. Ricketts and Stanislaus von Prowazek, two zoologist who died investigating a typhus epidemic in a prison camp in 1915.

Once these crucial facts were recognized, Rudolf Weigl in 1930 was able to fashion a practical and effective vaccine production method by grinding up the guts of infected lice that had been drinking blood. It was, however, very dangerous to produce, and carried a high likelihood of infection to those who were working on it.

A safer, mass-production-ready method was determined by Herald R. Cox in 1938, involving egg yolk, and this was tested and put into heavy use by 1943.

Epidemics

Epidemic typhus is responsible for a number of epidemics throughout history. It tends to follow after wars, famine and other problems that cause mass deaths (and therefore crowded conditions and lice).

References

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