Abstract:

Background: Cold storage facilities required for maintaining vaccine potency are largely inadequate in many low and middle income countries (LMIC). In this study, we have demonstrated the effect of ambient tropical storage conditions on stability and potency of Method: Newcastle disease virus (NDV) vaccine encapsulated in 1,2-dioleoyl-3-trimethyl ammonium propane (DOTAP) cationic liposomes. The liposomal vaccines were prepared using the thin-film hydration technique, and the biophysical characteristics were assessed. The cationic liposomes were stored at 28 oC or subjected to freeze-thaw cycles for 7 weeks and then reassessed for stability and potency using parameters such as particle size, polydispersity index, zeta potential, morphology, antibody titre as well as differential white blood cell count. Herts 33 velogenic strain of NDV was used as standard for challenge. Results: The liposomes exhibited spherical morphology when visualized using TEM. Malvern Zetasizer portrayed the liposomes as nanoparticles. Zetapotential and polydispersity indices were positive and below 0.1 respectively. The HI test revealed that the DOTAP cationic liposomes stimulated higher titres of antibodies when compared to the standard vaccine. Stability studies after 7 weeks of storage and freeze-thaw treatments showed slight aggregation as well as variations in particle sizes and distribution. The HI titer was, however, lower after secondary immunization with DOTAP cationic liposomes stored at 28 oC, but higher for the samples stored under freeze-thaw conditions. The immunized birds were 100 % protected from the virulent strain of NDV.