Immune Response of Pigs to Inactivated Foot-and-Mouth Disease Vaccines: Response to Emulsion Vaccines

Abstract

The serological response of pigs to inactivated single and double emulsion foot-and-mouth disease (FMD) vaccines has been examined. The slopes of the dose-response regression lines for types A, O and C vaccines were low and only small amounts of antigen were required to elicit good immune responses. These vaccines resulted in granuloma and abscess formation at the site of injection. The extent of this reaction was dependent on the volume of vaccine administered. A reduction in the dose volume from 2 ml. to 0.25 ml. did not influence the immune response. The intradermal inoculation of 0·1 ml. of a type A double emulsion vaccine stimulated acceptable concentrations of circulating neutralizing antibody with minimal tissue reaction. The duration of immunity produced by emulsion vaccines was good, with neutralizing antibody concentrations remaining above the 50% protection level for 210 days in the case of a type O vaccine and for 280 days for types C and A vaccines. Pigs immunized with an emulsion vaccine showed good anamnestic responses to both emulsion and saponin adjuvauted vaccines. IgM was present for 42 to 63 days after primary inoculation, while IgG appeared at about 21 days after vaccination.