Streptobacillus moniliformis

Streptobacillus moniliformis is a Gram-negative, pleomorphic, facultatively anaerobic bacterium. It is the primary causative agent of rat-bite fever, a disease that can result from a bite or scratch by infected rodents, or the ingestion of food or water contaminated with the bacterium. Streptobacillus moniliformis can also cause Haverhill fever, a similar condition that results from ingesting contaminated food or water. The bacterium is part of the normal respiratory flora of rodents, particularly rats, which serve as the primary reservoir for the pathogen.

Characteristics

Streptobacillus moniliformis is characterized by its ability to form chains of varying lengths in liquid media, a feature that contributes to its name (strepto- meaning chain, bacillus meaning rod-shaped). It does not form spores and is non-motile. The bacterium grows best at 37°C, in a pH range of 7.2 to 7.6, and requires enriched media with serum or blood for optimal growth. It is catalase-negative and produces acid from glucose fermentation.

Transmission

Transmission of Streptobacillus moniliformis to humans typically occurs through direct contact with the mucous membranes or broken skin via bites or scratches from infected rodents. Alternatively, ingestion of food or water contaminated with the bacterium can lead to infection. Person-to-person transmission is extremely rare.

Clinical Manifestations

The clinical manifestations of rat-bite fever vary but often include fever, chills, myalgias, arthralgias, and a maculopapular rash. If untreated, the infection can lead to more severe complications such as endocarditis, myocarditis, or meningitis. The incubation period ranges from 3 to 10 days for rat-bite fever and up to 3 weeks for Haverhill fever.

Diagnosis

Diagnosis of Streptobacillus moniliformis infection is challenging due to its nonspecific symptoms and the difficulty in culturing the bacterium. It often requires a high index of suspicion, especially in patients with a history of rodent exposure. Blood cultures, serology, and polymerase chain reaction (PCR) tests can be used to identify the bacterium.

Treatment

The treatment of choice for infections caused by Streptobacillus moniliformis is antibiotics. Penicillin is the most effective antibiotic, but for patients allergic to penicillin, doxycycline or erythromycin are suitable alternatives. Early diagnosis and treatment are crucial to prevent complications.

Prevention

Preventive measures against Streptobacillus moniliformis infection include controlling rodent populations, avoiding contact with rodents, and ensuring food and water are not contaminated with rodent excreta. In settings where exposure to rodents is unavoidable, protective clothing and gloves can reduce the risk of bites and scratches.