Lapin Challenge Model for Laboratory Development of an Oral Carbohydrate Based Vi Vaccine for Typhoid

A vaccine seed strainVSS of Salmonella enterica serovar typhoid was elected from local isolates of human enteric fever.A cell free culture fitrate antigen was prepared from VSS for in-vitro use.Vi antigen was separated,characterized from propagation of VSS in a suitable growth media.Incomplete Freund adjuvant IFA was as immune preconditionar and as immunostimlant.In three groups of rabbits each of five.First,saline control,second IFA preconditioned and the third was the Vi-IFA combination in which,the vaccine specific immune priming protocol was IFA through SC route to one week only.Followed by and oral 3mg/5ml dosages in a week a part for five weeks.Two to three days post to the sixth week dose,live S.typhi challenge dose of1.5/10 to five was applied per Os for the three groups.Saline control group got clinical infection, IFA group has shown 80% immune efficacy and the Vi-IFA group has shown 100% immune efficacy.Vi-IFA prototype experimental vaccine formulation proved to be;pure,safe, immunogenic,non-allergenic and immune effective against experimental live challenge.It induces humoral agglutinins , hem agglutinin and inhibits migration of leukocyte in capillary test.Confirmation of these findings in other nonhuman primate model is suggestive.