Rough leucine auxotrophic strains of Brucella expressing Salmonella flagellin C conjugated gonadotropins, an immunocontraceptive brucellosis vaccine for feral swine population control

Brucellosis, caused by Gram-negative bacteria of the genus Brucella, is a zoonotic disease with global impacts on human, livestock, and wildlife health. Around 500,000 cases of human brucellosis are reported by the World Health Organization annually. Even though brucellosis has been eradicated from domestic livestock in the United States of America, the causative bacterial pathogen is still present in elk, bison, and feral swine. With the growth of free-range farming, domestic livestock and wildlife populations come into close contact, spreading the disease. Feral swine interactions are of particular concern. They carry a number of zoonotic diseases including brucellosis. As there is no commercial vaccination protocol to prevent brucellosis in wildlife and swine, interactions with these populations are especially dangerous for public health. Feral swine population is increasing nationwide even with the current population control practices. There is an urgent need for efficient control of feral swine and preventing the spread of brucellosis. To aid in the prevention of the spread of feral swine across the USA, immunocontraceptives have been employed. Over the years several candidates have been tested, but the search for the perfect vaccine is still ongoing. The monumental task includes reversibly preventing one of life’s most basic necessities, reproduction, through an oral route with no effect on non-target species. One way that science is tackling both of these threats at once is through dual-purpose vaccines. Dual-purpose vaccines produce an immune response that targets two different pathogens, or in this case a pathogen and reproductive hormones. In the effort to produce this vaccine, more knowledge was needed in regards to B. neotomae. This dissertation showed that it has the ability to survive in a variety of cells from different species, in a similar manner to known virulent Brucella species. This is of concern when using B. neotomae as a vaccine, but it has also been shown that attenuated B. neotomae can provide protection against virulent B. suis, B. abortus, and B. melitensis challenge. This is a major finding in the effort towards a universal brucellosis vaccine. After genetic manipulation, cell culture assays, and mouse trials, several leucine auxotrophic B. neotomae and B. abortus strains show promise in the effort towards a dual-purpose vaccine. Strains of B. neotomae ΔwboA ΔleuB pNS4-trcD-fliC-Gonadotropins were discontinued in this effort towards a brucellosis immunocontraceptive dual-purpose vaccine due to lethality issues in mice. These stability and lethality issues are still under investigation. Instead, a proven stable strain of B. abortus RB51 (a USDA approved cattle vaccine) was used to investigate its effects on fertility in mice when expressing fliC-Gonadotropins. Strains B. abortus RB51 ΔleuB pNS4-trcD-fliC-porcineFSHβ (RB51LFSHβ) and B. abortus RB51 ΔleuB pNS4-trcD-fliC-GnRH (RB51LGnRH) confer reduced fertility characteristics in both male and female purpose bred mice. Strain RB51 ΔleuB has also been shown to protect against virulent B. abortus challenge in the literature. These findings warrant further investigation to determine the efficacy of these vaccine strains in swine as an oral vaccine. Ultimately, their ability to prevent brucellosis, while causing immunocontraception needs to be determined in feral swine.