Studies on vaccination against bacillary dysentery. 5. Studies in Erythrocebus patas

In earlier studies in man it has been demonstrated that streptomycin-dependent shigellae, if given orally in 5 sufficiently large doses, confer a very high type-specific protection against bacillary dysentery.In the present study, 2 groups of Erythrocebus patas monkeys were immunized with live streptomycin-dependent Shigella flexneri 2a, and a third group was not vaccinated. One of the vaccinated groups was given streptomycin with each dose of the live vaccine. The animals that received streptomycin with the vaccine were shedding these organisms in their faeces for a significantly longer period than the animals that did not receive streptomycin. A week after the last dose of vaccine, the animals were challenged with virulent Sh. flexneri 2a organisms. All the control animals developed diarrhoea and excreted challenge organisms for an average of 9 days. None of the 9 immunized animals showed pathological changes nor symptoms of dysentery. On average, they excreted challenge organisms for only 2.3 days.Immunological tests confirmed the immunity of the vaccinated animals.This study shows that 3 doses of live oral streptomycin-dependent Shigella vaccine given together with streptomycin are at least as effective as immunization with 5 doses of the same vaccine without streptomycin. Oral application of streptomycin, therefore, seems to have had an enhancing effect on the immunizing property of live oral streptomycin-dependent enteric vaccines.