The goal of the proposed research is the development of vaccines against Brucella infection that are safe and efficacious. Our general approach is focused on the use of live attenuated vaccines, LAVs. While vaccines developed from heat-killed organisms, crude extracts or recombinant subunits have demonstrated little efficacy, Brucella LAVs have proven highly effective when used in conjunction with test and slaughter. However, when applied to under-developed countries such programs can result in significant losses in animal productivity and family livelihood and as such enforcement is lax. Currently available Brucella vaccines are unsafe for use either directly in gestating animals or humans. Furthermore, their use in animals poses a secondary risk to public health especially in underdeveloped countries where livestock are a primary source of nourishment. For these reasons, we have sought to identify improved LAVs that are safe for use in animals at all stages of gestation, and, therefore, pose a reduced risk to humans. Ongoing experiments in nonhuman primates have confirmed a level of safety that provides continued support for a parallel goal of developing a Brucella vaccine that is safe for human use. Successful demonstration of safety in goats is also expected to provide support for reduced biocontainment level allowing examination of efficacy in goats. The overall design of the vaccine combines the optimal features of a LAV that is safe, free of side effects in animals and efficacious with a delivery system that provides enhanced immune stimulation through microencapsulation. The successful outcome of these studies will be used to produce a vaccine that provides significant protection against abortion and to enhance animal productivity while also restricting human infection including environmental contamination. However, drawbacks of live attenuated vaccines include the concern of reversion to virulence. For this reason, we have proposed an evaluation of secondary mutations that may be expected to effectively lock the organism into an attenuated state while providing a diagnostic test capable of distinguishing vaccines from infected animals. The need for improved Brucella vaccines is highly warranted due to continue human infection worldwide (500,000 new cases annually) resulting from close association with or consumption of agricultural animal products. Recent dramatic increases worldwide in wild and feral swine populations also act as reservoirs of human infection, as well as agricultural species. This concern is exacerbated by a lack of knowledge concerning mechanisms of immune protection and the potential use of Brucella spp. as bioweapons.
Brucella spp. is present in 86 countries in which tens of thousands of humans are treated for brucellosis annually. Historically a decrease in human infection has been shown to parallel the decline in animal disease. Animal vaccination performed in conjunction with test and slaughter campaigns has proven to be effective against human brucellosis. However, application of this approach in endemic areas has failed due to lax enforcement and the financial burden these places on families and the residual virulence of the currently available vaccine strains. The work proposed describes the development and evaluation of vaccine candidates with the potential to improve eradication efforts by preventing transmission associated with caprine abortion and subsequent spread of infection to other animals or humans.
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