Typhus is a rickettsial disease caused by one of two organisms, Rickettsia prowazekii (epidemic typhus and Brill disease) and Rickettsia typhi (murine or endemic typhus). Epidemic typhus and Brill disease are uncommon in the United States. Murine typhus occurs in the southeastern and southern states. There are less than 100 cases per year. Murine typhus is a milder form and is seldom fatal (less than 2%). It is frequently seen in the summer and fall and typically lasts two to three weeks. Risk factors for murine typhus include exposure to rat fleas or rat feces, or exposure to other animals (such as cats, opossums, raccoons, skunks, and rats). Epidemic typhus occurs in poor hygienic conditions (which is why it is sometimes called "jail fever"), usually when the temperature is cold. It is spread by lice. Although very rare in the United States, it has sometimes been spread by the lice and fleas of flying squirrels. Brill-Zinsser disease is a mild form of epidemic typhus, caused by reactivation of the disease in the body of someone who has been previously infected after a long period of dormancy. This is more common in the elderly.
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