Observations pointing to the conjunctiva as the portal of entry in salmonella infection of guinea-pigs

Abstract

In the course of salmonella epizootics in guinea-pigs due to Salm. enteritidis and Salm. typhi-murium, respectively, salmonella conjunctivitis was widespread, and conjunctival swabbing was found to be a more effective procedure for detecting the spread of infection than the examination of rectal swabs. Eye-swabbing with segregation of eye-positive guinea-pigs and their cage-mates was apparently successful in controlling two Salm. enteritidis epizootics.Later experimental observations showed that the conjunctival route was a far more effective one for producing systemic salmonella infection in guinea-pigs than the oral route. The 50% spleen infecting dose by the conjunctival route was of the order of 100 organisms, while a dose of 100,000,000 organisms of the same strain of Salm. enteritidis was ineffective by mouth. Blood-borne invasion from the primary conjunctival lesion occurred by the lymphatic route. Gut infection of guinea-pigs infected experimentally throughout the eye was secondary to spleen infection and probably occurred by excretion of salmonellae through the gall-bladder.The importance of the conjunctival route in natural salmonella infections of guinea-pigs was confirmed by goggling experiments, which showed that, except in animals with complicating conditions such as pregnancy, effectively goggled guinea-pigs were highly resistant to infection in environments heavily contaminated with Salm. enteritidis which produced high infection rates in ungoggled control animals.I am very grateful to my technician, Mr G. Sandys, for his enthusiastic help, particularly with the goggling experiments.