Immune response to potassium thiocyanate extract and toxoid vaccines of Pasteurella multocida in pigs

Abstract

The present study was undertaken with a view to evaluate the immunogenicity of the Potassium thiocyanate (KSCN) extract, toxoid and combined vaccines of Pasteurella multocida in pigs. The most immunogenic Pasteurella multocida capsular type A based on pathogenicity and toxigenicity was used for the study. The comparative immunogenicity of the vaccine preparations was determined by monitoring the corresponding serum antibody titres at different time intervals 0, 7, 21, 30, 45, 60, 75, 90 and 120 days post vaccination by Indirect haemagglutination test (IHA) and indirect ELISA. The serum antibody titres expressed in log2 value with KSCN extract and the toxoid vaccine when given in primary dose reached peak (10.12 ± 0.20 and 9.92 ± 0.24 respectively) by ELISA on 45th day, thereafter a decline in antibody titre was recorded up to 120 days post vaccination. However, the group given with combined primary vaccine revealed peak ELISA titre (10.32 ± 0.31) earlier on 30th day, 15 days earlier than KSCN and toxoid vaccines. With booster doses of KSCN extract and toxoid vaccines, the peak ELISA antibody titre (12.12 ± 0.37 and 11.72 ± 0.24) was recorded on 60th day. Similarly, the group receiving booster vaccination of combined vaccine showed its peak titre (13.13 ± 0.20) on 60th day and remained stable up to 75th day post primary immunization. IHA test also showed that piglets immunized with combined vaccine elicited higher antibody titre (10.40 ± 0.40) as compared to KSCN extract vaccine (9.20 ± 0.37) or toxoid vaccine (9.40 ± 0.24). Assay of Pasteurella-specific antibody by ELISA and IHA test showed a significant (p < 0.01) positive correlation between the tests. On statistical analysis, difference in ELISA antibody titre between the vaccines, day post immunization and nature of vaccination were found to be highly significant (p < 0.01). Combined booster vaccination was found to elicit higher antibody titre in pigs compared to KSCN extract or toxoid vaccines (p < 0.01).