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Rat-bite fever is an acute febrile illness that occurs as a result
of a rodent bite, usually a rat. Two distinct microorganisms, Streptobacillus moniliformis and Spirillum
minus, the agent of Soduka in Asia,1 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.1,2
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In addition to rat-bite fever, S moniliformis causes
an overlapping syndrome, Haverhill fever, also
known as erythema arthriticum epidemicum.1
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Sodoku, a disease reported in Asia that is currently
rare in the United States, is the name given to rat-bite fever caused
by S minus.
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S moniliformis is a normal 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.1,2 Approximately
50% of cases reported are in children. 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 Haverhill fever.1,3
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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 often, asymmetric polyarthritis4 that may
reflect sterile effusions or septic arthritis with S moniliformis present
in the joint fluid.5 Several days later there is
a maculopapular and sometimes petechial rash, which is most prominent
on the extremities, including the palms and soles.4 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. Left untreated, the
infection follows a relapsing course lasting a mean of 3 weeks,
but may have a fatal outcome1,6 or result in arthritis
persistent for several months. Other reported manifestations include
septic arthritis without a rash,5 amnionitis, brain
abscess, disseminated fatal infection in infants, endocarditis,
hepatitis, meningitis, myocarditis, nephritis, and pneumonia.1,6Patients
with Haverhill fever exhibit fever, rash, and arthritis; vomiting
and pharyngitis are more prominent than in patients with rat-bite
fever.
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Sodoku disease, due to S minus, has an incubation
period of 1 to 4 weeks. There is fever, ulceration at the previously
healed bite site, and regional lymphadenopathy. The fever may be
intermittent and associated with rash, with afebrile intervening
days. The infection responds rapidly to therapy with penicillin.1
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The diagnosis is established by recovering S moniliformis from
cultures of blood or joint fluid, but ...