Rat bite fever and Streptobacillus moniliformis

Abstract

Rat bite fever, caused by Streptobacillus moniliformis, is a systemic illness classically characterized by fever, rigors, and polyarthralgias. If left untreated, it carries a mortality rate of 10%. Unfortunately, its nonspecific initial presentation combined with difficulties in culturing its causative organism produces a significant risk of delay or failure in diagnosis. The increasing popularity of rats and other rodents as pets, together with the risk of invasive or fatal disease, demands increased attention to rat bite fever as a potential diagnosis. The clinical and biological features of rat bite fever and Streptobacillus moniliformis are reviewed, providing some distinguishing features to assist the clinician and microbiologist in diagnosis.

FIG. 1.

Gram-stained smear of S. moniliformis on blood agar medium, demonstrating pleomorphic gram-negative bacilli in chains and clumps with irregular, lateral bulbar swellings (photo courtesy of L. Wilcox, Hamilton Regional Laboratory Medicine Program, and D. Yamamura, Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada).

FIG. 2.

Petechial and purpuric lesions on the foot of a rat bite fever patient.

FIG. 3.

Hemorrhagic vesicles on the first and third toes of a patient with advanced rat bite fever.