Rat-Bite Fever

Abstract & Commentary

Synopsis: Two rapidly fatal cases of rat bite fever due to Streptobacillus moniliformis are described.

Source: CDC. Fatal Rat-Bite Fever—Florida and Washington, 2003. MMWR. 2005;53:1198-1202.

A 52-year-old female pet store employee presented to a Florida Emergency room with a 2-day history of a febrile illness. She was hypotensive and, despite receiving antibiotic therapy in an ICU setting, died within 12 hours of admission. Two months later, a previously healthy 19-year-old woman was dead on arrival at a Washington state hospital. Friends reported that she had had a febrile illness for the previous 3 days. The first patient had been bitten by a rat in her pet store 4 days prior to admission and the second lived in an apartment with 9 pet rats.

Peripheral blood smears of the 52-year-old woman revealed filamentous bacteria within neutrophils. Specially performed blood cultures yielded a bacterium that was biochemically identified as Streptobacillus moniliformis, with confirmation by 16S rRNA analysis. While postmortem blood and tissue from the 19-year-old were culture negative, clusters of filamentous bacteria were identified in sections of liver and kidney by use of a silver stain, and 16S RNA sequence amplification identified these organisms as S. moniliformis.

Comment by Stan Deresinski, MD, FACP

Rat bite fever caused by S. moniliformis typically begins with the abrupt onset of fever and chills, together with myalgias, arthralgias, and headache. An erythematous macular rash, most prominent on the extremities and involving the soles and palms, develops in most patients. Frank arthritis, most commonly affecting the knees, wrists, and elbows, may occur. Septic complications may occur at other sites. These include endocarditis, myocarditis, meningitis, and pneumonia. As in the 2 cases summarized here, the rapid onset of sepsis, culminating in death, may uncommonly occur. It is estimated that the case fatality in untreated patients is 10%. A similar illness, also called rat bite fever, is caused by a spirochet, Spirillum minus. This disease, almost exclusively identified in Asia, is also called sedoku.

S. moniliformis is a pleomorphic facultatively anaerobic Gram negative bacillus. Its morphologic variability in culture ranges from single cells to filamentous forms, which may resemble a string of beads as the result of central swelling of individual cells. In vitro cultivation requires supplementation with, eg, blood or serum. The CDC recommendations for diagnosis are contained in Table 1. S. moniliformis is part of the normal upper respiratory flora of rodents. One-third of patients do not have a history of a rat bite, and infection may occur as the result of non-bite contact with infected rats or their excreta. A form of illness called Haverhill fever (erythema arthriticum epidemicum) results from ingestion of the organisms, most frequently in contaminated raw milk.

Penicillin G remains the treatment of choice (see Table 1). The CDC lists tetracycline and streptomycin as alternatives.

These cases were identified by the CDC Unexplained Deaths and Critical Illnesses (UNEX) Project. UNEX coordinates surveillance for unexpected deaths possibly attributed to infection throughout the United States State and local health departments may contact UNEX for assistance with evaluation of unexplained deaths in their jurisdictions. Infectious disease clinicians should encourage them to do so.

Stan Deresinski, MD, FACP, Clinical Professor of Medicine, Stanford; Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center, is Editor for Infectious Disease Alert.