Zoom in on microorganisms

Germs that infect humans

Transmission of typhus

Transmission of typhus

© Illustration Bruno Laporte

Microorganism: the bacterium Rickettsia prowazekii

Disease: typhus

Occurrence of the disease

History: in 1906, Howard T. Ricketts discovered the bacteria responsible for typhus, which was transmitted by lice. While pursuing his work in the laboratory, and despite his careful technique, he was bitten while transferring some lice. In 1910, Ricketts died of typhus and the bacterium he studied was named Rickettsia in his honor.

Mechanism of action of the microorganism: as soon as the Rickettsia get into the bloodstream, they infect the cells of the blood vessels.

Symptoms of the disease: headaches, fever, muscle aches, and skin rashes.

Incubation period: one to two weeks, typically 12 days

Contagious period: transmission from humans to lice can occur between two to three days after the fever has diminished. The lice invariably die in the two weeks following the infection but their feces are only contagious between two and six days following ingestion of infected blood.

Hosts: humans, lice, and possibly squirrels

Transmission: the disease is transmitted through the bite of a rickettsia-infected louse. The bacteria contained in the contaminated feces of the louse enter the bloodstream at the site of the bite or of the injury caused when the person scratches himself. An infected person can then infect new lice, which can then continue to transmit the disease.

Treatment: antibiotics such as doxycycline, tetracycline, or chloramphenicol

Geographical distribution of the microorganism: louse-infected places, typically in certain mountainous regions of Mexico, Central and South America, central and east Africa, and in several Asian countries.

Prevention: reducing louse infestations with insecticides and minimizing contacts with infected people.

Vaccine: not available