Lack of Reactivation of Shigellosis in Naturally Infected Enrofloxacin-Treated Cynomolgus Monkeys After Exogenous Immunosuppression

Four cynomolgus macaques housed at our facility became acutely ill with dysenteric symptoms. Enteric isolates established an etiologic diagnosis of Shigella flexneri. Enrofloxacin antimicrobial therapy cleared the infection with no perceptible bacterial shedding or clinical signs of disease. High-dose methylprednisolone therapy was administered to the four monkeys for 5 weeks. The animals were monitored for signs of shigellosis and bacterial shedding weekly throughout the study, for a total of 7 weeks. Although methylprednisolone therapy induced marked cellular immunosuppression in all four animals, as measured by in vitro assays, no animal had evidence of clinical shigellosis or bacterial shedding. These results suggest that cynomolgus macaques naturally infected with S. flexneri and appropriately treated with enrofloxacin are unlikely to have reactivation of shigellosis and shedding of bacteria in the feces during periods of stress or profound immunosuppression.