Further questioning of the patient’s mother revealed she lived with 2 cats, 2 hissing cockroaches, 3 African frogs, 2 lizards, 1 mouse, and 10 rats. One of the rats bit her approximately 1 week prior to the onset of her symptoms. The rash improved, and after 7 days of intravenous antibiotic therapy the patient was discharged to her mother’s care with oral amoxicillin, to complete a 14-day course. A health department referral was initiated. She was seen for follow-up 2 weeks after discharge and was well.
Rat bite fever is rare in the United States, and accurate data about incidence rates are unavailable because the disease is not reportable in any state . Most cases in the United States are caused by S. moniliformis acquired through rat bites or scratches . The rate of nasopharyngeal carriage in healthy laboratory rats ranges from 10% to 100%, and that among wild rats is 50% to 100% [1,2].
Bites from mice, squirrels, and gerbils and exposure to animals that prey on these rodents (e.g., cats and dogs) have been associated with cases of rat bite fever . There have also been cases reported in which indirect contact, such as living in dwellings that are rat-infested or ingestion of water or food contaminated with rat feces, resulted in S. moniliformis bacteremia . Contamination of drinking water and raw milk has been linked to other cases . In 1996 two cases were linked to common exposures to the same dog and to consumption of surface water that could have been contaminated with rat feces .
The incubation period of rat bite fever caused by S. moniliformis can range from 1 to 22 days. Onset usually occurs 2 to 10 days after the rat bite. Clinical presentation is characterized by relapsing fever and asymmetric polyarthritis, followed by a maculopapular rash within 2 to 4 days on the extremities, palms, and soles. Other manifestations reported include headache, nausea, vomiting, myalgias, lymphadenopathy, endocarditis, meningitis, pneumonia, and focal abscess . Thirteen percent of untreated cases are fatal, but most cases resolve spontaneously within 2 weeks . Rat bite fever due to Spirillum minus occurs most commonly in Asia and has a longer incubation period, of about 1 to 3 weeks .
Diagnosis is made by blood culture only. The organism has strict growth requirements. It is slow-growing, and unless the laboratory is notified that Streptobacillus moniliformis is suspected, it is difficult for most laboratories to culture it . Serologic testing is no longer available.
Recommended treatment is with intravenous penicillin for 5 to 7 days, followed by treatment with oral penicillin for an additional 7 days. Tetracycline is an alternative agent that can be used when there is a history of penicillin allergy. There is limited experience with erythromycin, clindamycin, and ceftriaxone.
The pet history was not obtained until late in the course of this patient’s hospital stay. Initially, the patient denied having any pets at home because she was fearful they would be confiscated. The importance of obtaining a thorough history for a patient who presents with a fever and rash cannot be overemphasized.
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2. Centers for Disease Control and Prevention. Rat-bite-fever in a college student in California. MMWR Morb Mortal Wkly Rep. 1984; 33:318–320.
3. McEvoy MB, Noah ND, Pilsworth R. Outbreak of fever caused by Streptobacillus moniliformis. Lancet. 1987; 2:1361–1363.
4. Bignall J. Haverhill fever in Spain. Lancet. 1995; 346:632.
5. Rupp ME. Streptobacillus moniliformis
endocarditis: case report and review. Clin Infect Dis. 1992; 14:769–772.
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6. Centers for Disease Control and Prevention. Rat-bite-fever, New Mexico, 1996. JAMA. 1998; 279:740–741.