ABSTRACT
The purpose of this investigation was to relate cutaneous delayed hypersensitivity reactions to the degree of immunity induced in calves given a live virulent or a modified-live strain of Salmonella typhimurium. Calves were placed into 1 of 5 groups on the basis of the vaccinal strain given and route of the vaccination: (I) nonvaccinated controls, (II) vaccinated twice by IM inoculation with small doses of the live virulent strain, (III) vaccinated (IM) twice with the modified-live strain, (IV) vaccinated (orally) twice with the modified-live strains, and (V) vaccinated (IM, and then orally) twice with the modified-live strain. Skin testing was performed by intradermal injection of fragmented S typhimurium as antigen. Double skin fold thickness and visual assessments were recorded at 3, 6, 24, 48, and 72 hours after antigen was administered. Biopsy samples for histopathologic evaluation were obtained. After vaccination and skin testing were complete, calves were orally challenge exposed with 1.5 X 10(11) virulent S typhimurium. Cutaneous delayed-type hypersensitivity reactions (48 hours) were observed in all except controls (group I) and 2 of 3 calves vaccinated orally with the modified-live vaccine strain (group IV). Significant correlations between positive skin tests and protection from challenge exposure were observed except in group V calves, in which positive skin test results were seen, but adequacy of the immunity (or survival after challenge exposure) was inconsistent.
