Definition of Typhus:

Typhus is a bacterial disease spread by lice or fleas.

Causes, incidence, and risk factors:

Typhus is caused by one of two types of bacteria: Rickettsia typhi or Rickettsia prowazekii. The form of typus depends on which type of bacteria causes the infection.

Rickettsia typhi causes murine or endemic typhus. Endemic typhus is uncommon in the United States. It is usually seen in areas where hygiene is poor and the temperature is cold. Endemic typhus is sometimes called "jail fever." Lice and fleas of flying squirrels spread the bacteria.

Murine typhus occurs in the southeastern and southern United States, often during the summer and fall. It is rarely deadly. Risk factors for murine typhus include:

• Exposure to rat fleas or rat feces
• Exposure to other animals (such as cats, opossums, raccoons, skunks, and rats)

Rickettsia prowazekii causes epidemic typhus and Brill-Zinsser disease. Brill-Zinsser disease is a mild form of epidemic typhus. It occurs when the disease re-activates in a person who was previously infected. It is more common in the elderly.