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Streptobacillus moniliformis (Rat-Bite Fever)
Streptobacillus moniliformis, S. hongkongensis, and S. notomytis of the genus Streptobacillus cause infection in humans. They are fastidious, nonmotile, gram-negative, pleomorphic, and often filamentous, beaded, facultative anaerobic bacilli. S. moniliformis can exist in two phases: the bacillary phase and the cell wall-deficient L-phase. , In addition to being the main etiologic agent of a systemic illness called rat-bite fever , S. moniliformis causes Haverhill fever. Sodoku (spirillary rat-bite fever), an extremely rare disease in the US, is the name given to rat-bite fever caused by Spirillum minus, which manifests 1–4 weeks after a bite with relapsing fever, ulceration at the site of the bite, and associated regional lymphadenopathy. S. minus is a spiral gram-negative coiled bacillus with two or more helical turns and is motile. S. minus has not been isolated on solid media, and its diagnosis relies on visualization by darkfield microscopic examination of an ulcer or blood smear or on a Giemsa- or Wright-stained smear. This infection responds rapidly to therapy with penicillin.
Epidemiology
The natural habitat of S. moniliformis is the upper respiratory tract of rodents, including wild or laboratory rats as well as mice, gerbils, and squirrels, where carriage is common and asymptomatic. The organism can be excreted in rat urine. Humans are infected by the bite of a rat (or rarely mouse or squirrel) or, less commonly, from a scratch by a rat, from rat contact in the presence or absence of a break in the skin, from handling a dead animal, from skin injury from the cage of a rat, or from contact with a rat-eating carnivore such as a dog, cat, or weasel. , In some cases a pet rat had died recently of an unknown illness. Contact with pet rats account for most cases in some areas. In some persons with no history of rodent contact, infection may have been acquired through ingestion of milk or water contaminated with rat excreta, as occurred in epidemic form in 1916 in Haverhill, Massachusetts, and in the 1980s in England. , Approximately 50% of cases of rat-bite fever are reported in children.
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