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Despite extensive vaccination campaigns, Newcastle disease virus (NDV) remains endemic in many countries worldwide, and factors that contribute to this failure include mismatched vaccines, partial immunization, and poor husbandry practices. In order to overcome the problem of genetic divergence between circulating field strains and vaccine strains, we saponin-adjuvanted an Egyptian field strain and assessed its safety and immunogenicity in chickens. Immunization of chickens with the vaccine followed by challenge with a velogenic reference strain revealed the potential of the saponin-adjuvanted vaccine to induce a strong immune response that resulted in complete protection of chickens. Importantly, in vaccinated chickens, virus shedding was abolished, providing an added advantage over the currently available commercial live-attenuated and inactivated vaccines, which are unable to prevent shedding. A histopathological investigation demonstrated that the vaccinated chickens had less-severe lesions than challenged unvaccinated and mock-vaccinated chickens. We propose using this formulation as an alternative and improved NDV vaccine platform that can be exploited to control disease not only in Egypt but also in other disease-endemic countries.

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Corynebacterium ovis has a clear immunopotentiating effect when used as an adjuvant with several antigens including egg albumin, Salmonella typhimurium and foot and mouth disease virus, inoculated into guinea pigs. The optimal dose was found to be 400 mg of C. ovis mixed with antigen. However, a dose of 300 mg of C. ovis when mixed with incomplete Freund's adjuvant was enough to stimulate a sustained potent immune response which was superior to that obtained with the complete Freund's adjuvant. Immunopotentiation is a topic in immunology that is attracting increasing interest. In this field, oil adjuvants have proved their superiority and Freund et al. (10) have shown that the addition of some bacteria, such as mycobacte ria, to such oil adjuvants improves their immunopotentiating effect. Current studies carried out in our laboratory on crystal violet treated C. ovis have clearly shown its capacity as a non-specific immune stimulant, capable of raising the resistance of sheep to artificial infection with potential pathogens, in a manner comparable with that produced by BCG (5, 6). It was decided to test the formalin-killed C. ovis for its immunopotentiat ing ability when used as an adjuvant with inert antigens and killed microbial vaccines. MATERIALS AND METHODS Animals. Guinea pigs : 630 healthy albino adult guinea pigs, weighing approxim ately 400-500 grams, were used in this study. The animals were put in equal * Under-Secretary of State for Veterinary Affairs, Egypt.