The guinea pig as a model for the asymptomatic human typhoid carrier

Studies were designed to develop an animal model which mimics the asymptomatic carrier state of typhoid fever, Salmonella typhi infection, in man. The gallbladder of the guinea pig [Can (HA)] was surgically cannulated to provide a route for infection and bile sampling. Organisms (2 X 10(8) S typh:) were introduced by way of the cannula and samples of bile removed and analyzed periodically. Salmonella typhi was recovered from the bile and feces of infected, yet apparently normal, guinea pigs for periods of up to 5 months thus mimicking the human symptomeles carrier. Some guinea pigs were treated with chloramphenicol after infection. Antibiotic therapy with chloramphenicol did not eliminate the carrier state. Microabscesses of the liver were induced by S typhi both in untreated and treated animals (cultures were positive from these abscesses). When blood antibiotic levels dropped, the organism was found in the bile fluid and was again excreted. Vaccinated guinea pigs developed elevated levels of 0 and H serum antibody, but were not protected against infection of the gallbladder with S typhi (2 X 10(8) organisms). Similarly, vaccination failed to eliminate the carrier state.