Trehalose improves PPR vaccine virus stability in diluent

Abstract

Background: Specialized freeze-drying process is being used in the field for different thermostable vaccine preparation worldwide. The thermostability remains only in undiluted conditions. If dilution is made at the morning and used for the whole day, the vaccine efficacy is compromised at high ambient temperature. In this study, trehalose based specialized vaccine diluent was used to improve the stability of Peste des Petits Ruminants (PPR) vaccine in diluted condition. Methods: The available PPR vaccine was reconstituted with conventional diluent and with trehalose based test diluent. The diluted vaccine was kept at ambient temperature without maintaining any cool chain. Stability of diluted vaccine virus was further assessed in vivo and in vitro at different temperatures. Goats were vaccinated and Vero cells were infected with reconstituted vaccines and were assessed at 0, 3, 6, 9 and 24 hours post dilution. Antibody titer was measured and virus infectivity titer was determined in both cultured cell lysate and supernatant. The presence of the virus particles in Vero cell was confirmed by standard RT-PCR targeting Fusion (F) gene of PPR virus. Results: In vivo results revealed that the number of goats possessed antibodies to PPR virus was higher in trehalose based vaccine formulation than the conventional PBS based diluent. Reconstituted vaccine virus (using PBS and trehalose diluent) infected Vero cells produced 70-80% cytopathic effect (CPE) in 5th days of post infection. Both diluents produced and maintained infectivity titer from log10 TCID50 5.5 to log10 TCID50 3.6, until the use of vaccines incubated for 9 hours after dilution. On the other hand, at 24 hours of post dilution only trehalose formulated vaccine produced log10 TCID502.5 whereas no infectivity titer was observed at the same time using conventional one. Conclusion: The present study suggests that trehalose preserves the quality of reconstituted vaccine in terms of infectivity titers. Trehalose can be a diluent of choice for reconstitution of PPR vaccine in field.