Case Report and Treatment of Streptobacillus moniliformis in Laboratory and Wild Thirteen-Lined Ground Squirrels (Ictidomys tridecemlineatus)

Streptobacillus moniliformis is a Gram-negative bacterium and the causative agent of rat bite fever. In 2020, members of a laboratory-born thirteen-lined ground squirrel (Ictidomys tridecemlineatus) colony tested positive for S. moniliformis during routine pathogen screening at the University of Wisconsin–La Crosse. These animals were asymptomatic and continued to be monitored and tested until treatment was attempted with tetracycline in May 2023. Two different treatment regimens were attempted. Squirrels treated with 10-mg treats twice daily for 7 to 10 d were no longer positive for S. moniliformis. New squirrels entering the University of Wisconsin–La Crosse animal facility were tested. The only additional positive case was in a wild-caught thirteen-lined ground squirrel in 2024. This squirrel subsequently tested negative following the same tetracycline treatment. Based on the identification of this zoonotic agent in both laboratory and wild-caught species, we recommend regular screening for S. moniliformis in captive squirrels and prudent management decisions when handling these animals and their waste. To our knowledge, this is the first published report of confirmed S. moniliformis in squirrels.