Preparation of an Inactivated Peste des Petits Ruminants Vaccine and Its Comparative Immunogenicity Evaluation in an Animal Model

Peste des petits ruminants (PPR) is a highly contagious disease that is considered a major threat to the small livestock industry. Although vaccination via live-attenuated PPR vaccine is a main controlling strategy in the endemic area, during PPR eradication process, the inactivated PPR vaccine (iPPRV) is recommended. This study aimed to compare the inactivation kinetics of the PPR virus via different inactivants and immunogenicity evaluations of the iPPRV formulated vaccine in mice. The vaccinal live PPR virus was inactivated by either H2O2 or binary ethylenimine (BEI (at two concentrations of 1 or 4 mM. Thereafter, the inactivated virus was formulated with different adjuvants, including aluminum hydroxide (AH), aluminum phosphate (AP), and a mixture of AH and AP that were intraperitoneally (IP) administrated (0.1 mL) to 90 BALB/c mice in a completely randomized design and 3×3 factorial arrangement (9 animals per group). The booster vaccination was carried out in all animals 21 days after the primary vaccination. Results showed that the PPR virus was successfully inactivated by all the inactivation agents; however, the time of complete virus inactivation was estimated to be 482, 295, and 495 min post-treatment initiation for 1 mM BEI, 4 mM BEI, and H2O2, respectively. The main effect of inactivant on antibody titers against PPR virus that was measured after 42days post-immunization in mice was significant (P<0.05); however, the adjuvant and interaction effect of inactivator×adjuvant were not effective(P>0.05). Inactivation by 1 mM BEI was associated with a higher antibody titer against PPR virus (P<0.05) in comparison with both 4 mM BEI and H2O2 (2.51 vs. 2.25 and 2.22, respectively). Meanwhile, there were no significant differences among the used adjuvants in terms of eliciting antibody response against PPR virus. In conclusion, the use of 1 mM BEI in combination of AH, AP, or a mixture of AH and AP was associated with a higher immune response against PPR virus in mice. However, the appropriate inactivation kinetic of the virus and immunogenicity associated with the use of H2O2, as well as its biocompatibility property and better cost-benefit, nominated H2O2 to be used in iPPR preparation; however, more investigations are required in target animals.