Stability and Immune Responses of a Newly Formulated Thermo-Tolerant Peste Des Petits Ruminants Virus Vaccine
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Date
2024-09
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Kenyatta University
Abstract
Peste des Petits ruminants (PPR) is an acute and contagious viral disease of small ruminants (goats and sheep) with a registered high morbidity and mortality rate levels in naive populations. The disease is largely endemic in most Asian and African countries and is known to cause annual losses of approximately USD 1.45-2.1 billion affecting 330 million individuals of the world’s poorest 76 countries. Peste des petits ruminants virus is a highly infectious transboundary disease with no treatment and can only be sustainably controlled through vaccination. Small ruminants often play a fundamental role in the livelihoods of pastoralists as they act as a source of food and are sold off quite often to meet daily financial needs. Small ruminants require fewer resources, reproduce faster, and are more resistant to environmental shocks and hence are more relied on than large ruminants. The current conventional PPRV vaccines are thermo-labile and require to be kept at 2°C - 8°C for them to remain viable during storage and transportation. This present study was aimed at evaluating the stability and immune response of a newly formulated thermo-tolerant PPRV vaccine. The study prepared PPRV vaccine cultures using live attenuated PPR vaccine (N75/1), Sucrose, and Trehalose sugars augmented with proteins (lactalbumin hydrolysate (LAH)) and adopted the Xerovac lyophilization technique. Comparative analysis of the thermotolerance of both vaccines was assessed using the Accelerated Stability Tests (ASTs) at different temperatures (25°C, 37°C and 40°C). The ability of the vaccine to elicit PPRV neutralizing antibodies was determined in rabbits. Serum samples were collected weekly from day 0 to day 28 and on day 42 and 56 and IgG antibodies were quantified by competitive enzyme linked immunosorbent assay (c- ELISA). Data were analyzed using the GraphPad Prism software and utilized Spearman-Karber, regression analysis, t-test, and One Way Analysis of Variance (ANOVA) statistics. A P values ≤ 0.05 was considered statistically significant. The vaccine shelf life was determined as the time the vaccine retained its minimum infectivity dose at a specified temperature excursion. Results indicated that, the vaccines produced using Trehalose + LAH stabilizers were the most stable across all three temperature ranges. The shelf life of the trehalose-based vaccine was 21 days at 25°C, 19 days at 37°C, and 5 days at 40°C. There was a significant difference (p=0.0001) in vaccine degradation at 25°C and at 37°C. Comparative thermo- degradation analysis between the newly formulated thermo-tolerant and the conventional thermo-labile PPRV vaccines showed a significant difference (p=.0001) in thermo-tolerance across the two temperatures (25°C and 37°C). There was also a significant difference (p=0.116) in vaccine degradation at 40°C. Vaccinated rabbits showed protective antibodies for the 56 days of observation period. The study concludes that the use of trehalose and sucrose can provide successful thermo- stabilization of vaccines while eliminating use of expensive cold chain systems during storage, transport, and field application. It is recommended that sugar-stabilized PPR vaccines can be used to facilitate successful mass vaccinations in the tropical regions as part of the global PPR eradication.
Description
A Research Thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of Master of Science (Microbiology) in the School of Pure and Applied Sciences of Kenyatta University September, 2024
Supervisors:
1.Anthony Kebira
2.Irene Ogali