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Appl Environ Microbiol. 1970 November; 20(5): 770-774
Copyright © 1970 American Society for Microbiology. All Rights Reserved.

Quantitation of the Antigenicity and Immunogenicity of Purified Foot-and-Mouth Disease Virus Vaccine for Swine and Steers

Plum Island Animal Disease Laboratory, Animal Disease and Parasite Research Division, Agricultural Research Service, U.S. Department of Agriculture, Greenport, New York 11944

ABSTRACT

The antigenicity and immunogenicity of a purified preparation of foot-and-mouth disease virus [type A₁₂, strain 119 (FMDV A-119)] inactivated with 6.0 mMN-acetylethylenimine at 37 C were compared in swine and steers. Three antigen doses were tested, 640, 160, and 40 ng. In accordance with findings for guinea pigs, as previously determined by dose-response curves, as little as fourfold changes in antigen in the region of the minimum effective dose produced marked differences in the serological and immune responses of swine. The minimum effective dose of antigen for antibody formation in swine and guinea pigs, as determined by mouse median protective dose (PD₅₀) values, was 160 ng. The minimum immunogenic dose for swine was also 160 ng. The vaccinated swine were challenged with either FMDV A-119 or with heterologous subtype A₂₄ strain Cruzeiro or type A strain A-CANEFA-1. Those immunized with 640 ng of antigen were about equally immune to the three challenge viruses; most swine having a mouse PD₅₀ value of 2.0 or greater were immune regardless of which strain was used for challenge. In steers, the smallest dose tested, 40 ng, was satisfactory in eliciting circulating antibodies and immunity. Physical and biological tests indicated that the antigen used in the vaccine is stable for at least 9 months at 4 C.

¹ Present address: Department of Veterinary Science, University of Kentucky, Lexington, Ky. 40506.