Rat bite fever is an acute, rare disease caused primarily by the bacterium Streptobacillus moniliformis. In some parts of the world, particularly Asia, Spirillum minus causes spirillary rat bite fever. Rats can carry these bacteria but generally do not show any signs of illness. The majority of cases are due to the animal's bite. It can also be transmitted throughout food or water that is contaminated with rat feces or urine. It is diagnosed by detecting the bacteria in skin, blood, joint fluid, or lymph nodes. People who keep rats as pets, laboratory technicians and pet shop employees working with rats, are at increased risk of infection.
Symptoms of the streptobacillary form include recurrent fever, rash, and arthralgias. The spirillary form causes relapsing fever, rash, and regional lymphadenitis. Symptoms usually occur 3-10 days after exposure to an infected rat, but can be delayed as long as 3 weeks for the spirillary form. Rat bite fever can be treated readily with penicillin and tetracyclins, but untreated S. moniliformis infections are estimated to be fatal and may cause complications like infection of the brain or soft tissue, infection of the heart valves, inflammation of the parotid glands, the tendons and the heart lining.