Rat-Bite Fever

Ralph D. Feigin

Mark E. Helm

Rat-bite fever describes either one of two distinct clinical syndromes. Streptobacillary rat-bite fever is reported more commonly in North America, whereas spirillary rat-bite fever, also called soduku, appears more often in Asia. Either form is transmitted by the bite of a rat or other rodent or by contact of the skin or mucous membrane with an infected animal. Transmission of the streptobacillary form to humans from mice, squirrels, weasels, gerbils, and domestic animals that prey on rodents also has been reported. The causative agent of streptobacillary rat-bite fever also can be transmitted by ingestion of contaminated water or unpasteurized milk products. The illness that occurs after such ingestion is called Haverhill fever, and it may appear as epidemic outbreaks. Rat-bite fever is considered a rare disease, with incidence dependent on contact with rats or other carriers. The true incidence is unknown, and the condition likely is underdiagnosed.

CAUSATIVE AGENTS

Streptobacillus moniliformis causes streptobacillary rat-bite fever and Haverhill fever in humans. This nonencapsulated, nonmotile, gram-negative rod is pleomorphic and fastidious, but it can be grown on current culture media supplemented
with serum, ascitic fluid, or blood. In vitro growth may be inhibited by sodium polyanethol sulfate found in most aerobic, but not anaerobic, blood culture bottles. S. moniliformis may produce variants without cell walls in the presence of penicillin or suboptimal growth conditions, but these forms usually revert under appropriate conditions to parent forms. These L-phase variants are resistant to penicillin, may deposit in tissues, and may prolong duration of symptoms of infection.

Spirillum minus, responsible for the spirillary form of rat-bite fever, is a 2- to 5-μm aerobic gram-negative spirochete with a terminal flagellum. Researchers generally agree that this organism, like other spirochetes, cannot be grown on artificial media.

CLINICAL MANIFESTATIONS

The clinical manifestations of the two forms of rat bite fever caused by S. moniliformis and that caused by S. minus are shown in Table 172.1.

TABLE 172.1. CLINICAL FEATURES OF RAT BITE FEVER

Streptobacillus Moniliformis	Streptobacillus Moniliformis	Spirillum Minus
Streptobacillary Form	Haverhill Fever Form	Spirillum Minus
Incubation period of 1–10 days (usually <7)	Incubation period of 1–3 days	Incubation period of 14–18 days
Fever	Fever	Induration at site of inoculation
Chills	Chills	Lesion may progress to ulcer and eschar
Headache	Rash	Fever
Vomiting	Arthritis	Chills
Maculopapular rash (2-4 days after disease onset; rash may become petechial or purpuric and desquamate)	Upper respiratory illness Gastrointestinal complaints	Regional lymphadenopathy (common)
Septic arthritis		Relapses (common)
Lymphangitis, lymphadenitis (rare)		Rash: purple to red brown with
Endocarditis		occasional indurated erythematous
Pneumonia		plaques
Relapses (rare)		Severe diarrhea (common)
		Weight loss (common)
		Anemia (common)
		Meningitis
		Endocarditis
		Myocarditis
		Nephritis
		Hepatitis