What Is Typhus and How Do You Get It?

I've been reading about a typhus outbreak in Los Angeles recently, and it sounds like a horrible disease. What causes typhus? Is typhus contagious? How do you get typhus?

Typhus is a disease caused by bacteria (mainly Rickettsia typhi or R. prowazekii). There are two major types of typhus: endemic (or murine typhus) and epidemic typhus -- bacterial infections cause both. The bacteria are small and very difficult to cultivate. Originally, they were thought to be viruses. The disease occurs after bacteria (Rickettsia) transfer to humans, usually by vectors such as fleas or lice that have acquired the bacteria from animals such as rats, cats, opossums, raccoons, and other animals.

Endemic typhus (mainly caused by R. typhi) is also termed murine typhus and "jail fever." "Endemic typhus" also means that an area or region has an animal population (usually mice, rats, or squirrels) that has members of its population continually infected with R. typhi that through flea vectors can incidentally infect humans. Epidemic typhus (caused by R. prowazekii) is the more severe form of typhus. It has also been termed recrudescent or sporadic typhus. "Epidemic typhus" also means that a few animals, (usually rats) via lice vectors, can incidentally infect large numbers of humans quickly when certain environmental conditions are present (poor hygiene, crowded human living conditions) with the more pathogenic R. prowazekii. Epidemic typhus has a milder form termed Brill-Zinsser disease, which occurs when R. prowazekii bacteria reactivate in a person previously infected with epidemic typhus.

How do you get typhus?

The causes of typhus are small Gram-negative coccobacilli-shaped bacteria, members of the genus Rickettsia that are intracellular parasites of many animals and utilize the components within the cell to survive and multiply. Typhus is sometimes generally labeled as flea-borne, tick-borne typhus, or louse-borne typhus, depending on the vector that transmits the bacteria. They are difficult to cultivate because they usually only grow within cells they infect. Occasionally, the bacteria may become dormant in infected cells, and years later, again begin to multiply (causing Brill-Zinsser disease). Generally, typhus follows an animal (rat, mouse) to vector (louse, flea) cycle. Humans are incidentally infected usually when the vectors come in close proximity to humans. The two Rickettsia species responsible for the two main types of typhus are Rickettsia prowazekii, the cause of epidemic typhus, and R. typhi, the cause of endemic typhus. However, R. felis, another species usually found in cat and cat fleas (Ctenocephalides felis), has been linked to people with endemic typhus also. Epidemic typhus usually spreads to humans from body lice (Figure 1) feces contaminated with R. prowazekii or occasionally from animal droppings contaminated with these bacteria. Endemic typhus usually spreads to humans by flea feces or animal droppings containing R. typhi or R. felis. The flea or louse (Pediculus humanis) bite causes itching and scratching and may allow the bacteria to enter the scratch or bite area in the skin. Indirect person-to-person transmission of rickettsiae can occur if lice or fleas infect one person who develops the disease and then the infected lice or fleas move from person to person by direct contact or via shared clothing. In general, head lice that differ from body lice do not transmit Rickettsia.

Read our full medical article for more information about typhus.