Oral Vaccination against Tularemia in the Monkey

Studies on the immunogenicity of live tularemia vaccine for animals and man vaccinated dermally or aerogenically were sufficiently encouraging to warrant an evaluation of vaccination of the monkey via the oral route. A preliminary investigation of the oral infectivity and virulence of P. tularensis SCHU S4, fatal for the monkey infected dermally or by the respiratory route with 10-25 organisms, revealed that 104 viable cells swallowed with milk did not result in infection but that 106 organisms infected two of eight animals, both of which died. An oral dose of 108 or 1010 cells infected all monkeys tested and the majority died; severe inflammation and ulceration of the gastrointestinal tract were found at necropsy. The course and outcome of the disease were comparable when animals were compelled to swallow intact a gelatin capsule containing 1010 organisms.