Severe recurrent Streptobacillus moniliformis endocarditis in a pregnant woman, and review of the literature

Background: Rat bite fever is a systemic febrile illness caused by infection with the Gram-negative bacillus Streptobacillus moniliformis following a bite, scratch, or contact with excrement. Only 26 cases of native valve endocarditis have been reported to date. We could find no other reports of severe Streptobacillus endocarditis requiring valve replacement in a young, pregnant patient.

Case presentation: A pregnant patient sought care for right leg pain, fevers, left upper quadrant pain, generalized weakness, fatigue, and inability to bear weight on her right leg. She had a syncopal episode 9 months earlier, resulting in a mandibular fracture and internal fixation hardware. Her pregnancy was complicated by hyperemesis and weight loss. Her pets included a rescued wild bird, a cat, and four rats. Her parents rescued stray cats, and she recalled multiple cat bites and scratches since childhood. She denied injection drug use. Ultrasound indicated a right popliteal artery thrombus. Transesophageal echocardiogram revealed a 2 cm × 0.7 cm vegetation. Angiography demonstrated multiple splenic infarcts and bilateral renal infarcts. She underwent mitral valve repair. The mitral valve Gram stain demonstrated 2+ Gram-negative rods, rare Gram-positive rods, and moderate white blood cells. Propionibacterium spp. was isolated from the mitral valve tissue on Columbia agar incubated anaerobically. Anaerobic and aerobic cultures of the valve tissue on all other broths and agars remained negative at 14 days. Hematoxylin and eosin stains showed a fibro-inflammatory vegetation. Aggregates of rod-shaped bacteria were identified on Warthin Starry/Steiner stain. Bartonella titers were positive for B. henselae IgG 1:256, IgM < 1:20. Brown-Hopps Gram stain, AFB, and GMS stains for bacterial and fungal microorganisms were negative. Broad range bacterial PCR and sequencing of a segment of 16 s rRNA gene of the valve tissue matched to Streptobacillus sp. (genus level) and most closely related to Streptobacillus moniliformis.

Conclusion: This case demonstrates diagnostic and therapeutic challenges associated with a relatively uncommon cause of endocarditis. The diagnosis of rat bite fever was delayed due to symptoms of a concomitant pregnancy. Other confounders included possible alternative sources or co-infections with another zoonosis from multiple pets, and an odontogenic source due to presence of exposed jaw hardware.

Keywords: Endocarditis; Pregnancy; Pregnant; Rat bite fever; Streptobacillus moniliformis.