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Rat-bite fever is an acute febrile illness with arthritis and rash that occurs as a result of the bite of a rodent, usually a rat. Two distinct microorganisms, Streptobacillus moniliformis and Spirillum minus, the agent of sodoku in Asia, cause this infection.


S moniliformis, the main etiologic agent of rat-bite fever, is a fastidious, gram-negative, pleomorphic, and often filamentous and beaded facultative anaerobic bacillus. In addition to rat-bite fever, S moniliformis causes an overlapping syndrome, Haverhill fever, also known as erythema arthriticum epidemicum. A second Streptobacillus species, S hongkongensis, has been described to cause a rat-bite fever-like syndrome not associated with rat contact. Sodoku caused by S minus is currently rare in the United States.

S moniliformis is a normal and asymptomatic inhabitant of the upper respiratory tract of rodents and may be excreted in rat urine. Humans are infected by the bite of a rat (or mouse, squirrel, cat, or weasel) or, less commonly, by a scratch from a rat, by handling a dead animal, or by contact with rat-eating carnivores. Approximately 50% of cases reported are in children, and pet rats are a source of infection. Infection may also be acquired by ingestion of milk or water contaminated with rat excreta, as occurred in epidemic form in 1916 in Haverhill, Massachusetts, resulting in the name “Haverhill fever.”


Seven to 10 days (range 2–21 days) after a rat bite, there is an abrupt onset of fever accompanied by chills, headache, vomiting, muscle pain, and sore throat. Fifty percent develop asymmetric polyarthralgia or polyarthritis typically involving the knees and ankles that may reflect either sterile effusions or septic arthritis with S moniliformis present in the joint fluid. Several days later, there is a maculopapular and sometimes petechial, pustular, or purpuric rash, which is most prominent on the extremities, including the palms and soles. The bite wound has usually healed, and the site exhibits no or minimal inflammation. Generalized adenopathy commonly occurs. Young children often have diarrhea and weight loss. Many of the clinical features are similar to Rocky Mountain spotted fever and disseminated gonococcal infection. Left untreated, the infection follows a relapsing course lasting a mean of 3 weeks, but may have a fatal outcome or result in arthritis persistent for several months. Other reported manifestations of S moniliformis infection include fever without a focus, osteomyelitis, septic arthritis without a rash, amnionitis, brain abscess, disseminated fatal infection in infants, endocarditis, hepatitis, meningitis, spinal epidural abscess, brain abscess, cutaneous abscess, myocarditis, nephritis, and pneumonia. Patients with Haverhill fever exhibit fever followed by rash and polyarthritis/polyarthralgia; vomiting and pharyngitis are more prominent manifestations than in patients with rat-bite fever.

Sodoku disease, due to S minus, has an incubation period of 1 to 4 weeks. There is fever that may be relapsing, ulceration at the ...

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