Evaluation of the Safety and Immunogenicity of Saponin-, Heat-, and Minor Formaldehyde-Inactivated Contagious Caprine Pleuropneumonia Whole Culture Vaccine
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Date
2022
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Addis Abeba University
Abstract
Contagious caprine pleuropneumonia (CCPP) is a fatal disease of goats imposing significant economic losses through the goat production system. Addressing effective vaccine is the most cost-effective technique in the control of the disease. In National Veterinary Institute (NVI), inactivated protein-based Mycoplasma capricolum subspecies capripneumoniae (Mccp) F-38 strain whole culture vaccine is in use since a few years ago. The vaccine is inactivated by formaldehyde (in a 0.5% proportion) and adjuvated with saponin. Despite the efficacy of the vaccine in Ethiopia, using saponin and heat inactivation has not yet been well considered. While saponin could be used both as inactivant and adjuvant simultaneously, extra formaldehyde is applied for inactivation. This could affect the immunogenicity of the vaccine, and it is not economical to invest on extra formaldehyde. Formaldehyde also has a residual effect. In addition, it is toxic to the laboratory workers, while heat treatment is relatively safer and cheaper. On the other hand, applying high amount of formaldehyde affects the immunogenicity of the vaccine. The aim of this study, therefore, was to evaluate the safety and immunogenicity of the vaccine inactivated alternatively by saponin and heat to replace formaldehyde inactivation, and by minor amount of formaldehyde to make use of such amount in the inactivation process of the vaccine. The vaccine was prepared using World Organization for Animal Health (OIE) guideline for CCPP vaccine production and the standard operating procedure of the manufacturer, NVI. The prepared Mccp culture aliquots were inactivated separately by saponin, heat treatment, and minor formaldehyde proportion. Thirty Mccp antibody-free goats were arranged into 5 groups, and a single dose of every vaccine formulation of a different inactivant was applied to each respective group. The goats were observed for 1 month for the safety and immunogenicity evaluation. All of the inactivation protocols were effective in inactivating the vaccine, and the respective vaccine preparations were safe. While the preparations inactivated by heat and 0.1% formaldehyde showed seroconversion values of equal significance with that of the conventional vaccine (p > 0.05), the saponin-inactivated vaccine brought unsatisfactory results. Accordingly, it was concluded that after a field trial and/or challenge study, heat and 0.1% formaldehyde, but not saponin, can be applied as alternative inactivating agents for the CCPP whole culture vaccine, which may improve the vaccine quality and occupational safety.
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Keywords
CCPP, goat, inactivant, vaccine