Occupational Health & Safety

Shigellosis

Nonhuman primates are the only important reservoir for Shigella infection in animal facilities, although zoonotic transmission of the organism from other laboratory research animals has been recorded under unique circumstances. Nonhuman primates can harbor several Shigella spp. that are pathogenic for humans, including S. flexneri, S. sonnei, and S. dysenteriae.

Infection with the gram-negative, non spore-forming bacilli of Shigella spp. is extremely common among nonhuman primates. The most frequently found species is Shigella flexneri. Shigellosis is the most frequently identified cause of diarrhea in these animals, and is a significant zoonotic disease. Acute shigellosis in nonhuman primates is often fulminant and fatal. It is characterized by diarrhea with mucus and blood, prostration, edema of the face and neck, and rectal prolapse. Animals that recover from an episode often remain asymptomatic carriers and, although they may have negative fecal cultures, they may also have recurrent acute episodes in times of stress.

The disease in people, like that in nonhuman primates, varies from the completely healthy asymptomatic carrier state to a severe dysentery syndrome with bloody mucoid diarrhea, abdominal cramping, tenesmus, anorexia, and weight loss. Shigella organisms, which may be present in the feces, and rarely in the blood, of infected individuals, are spread primarily by the fecal-oral route. The infectious dose is very small. The ID25-ID50 of Shigella flexneri for humans is reportedto be approximately 200 organisms. Very minimal contact between infected animals and humans has been incriminated in fatal disease.

Animal Biosafety Level 2 facilities and practices are recommended for infected animals. Access of personnel to areas where there are animals with shigellosis should be minimal. Those who work with infected animals should especially observe enteric precautions with good personal hygiene and thorough hand washing. It has been recommended that all newly arrived nonhuman primates be screened for Shigella infection so that asymptomatic carriers can be treated to prevent spread in the colony.