Attempted oral vaccination of swine with Brucella neotomae for protection against subsequent challenge with Brucella suis

Abstract

As part of a program to develop an oral vaccine for the control of brucellosis in feral swine, 64 pregnant, domestic swine were orally exposed to Brucella neotomae and subsequently conjunctivally challenged with Brucella suis. In an effort to reduce the number of swine shedding viable Brucella sp. bacteria at any one time, two sets of swine were used in this experiment. The first set of swine consisted of 17 vaccinated and 17 non-vaccinated control animals. The second set consisted of 15 animals in each group. The vaccination procedure involved feeding the animals to be vaccinated a standard swine ration mixed with approximately 1x10¹³ colony forming units (CFU) of B. neotomae per gilt daily for 3 days, with a total average dose of >4x10¹³ CFU of B. neotomae per gilt. All animals were challenged via bi-lateral conjunctival inoculation with approximately 1x10⁷ CFU of B. suis Strain 1330 per gilt. As many gilts as possible were euthanatized and necropsied within eight days prior to their expected date of parturition. Selected tissue samples were collected from all adults and their offspring and cultured on selective media for the isolation and identification of Brucella sp. Eight vaccinated and seven non-vaccinated control animals from the first set of gilts were determined to have been infected with B. suis. None of the gilts in the second set of animals or any of their offspring were determined to have been infected with B. suis. Data from the two sets of animals were not combined. No clinical signs that could be definitively attributed to brucellosis were seen. In contrast to previous studies, there was no evidence in this experiment that oral exposure to B. neotomae protects swine against infection resulting from subsequent conjunctival exposure to B. suis. This may have been a result of failure to provide sufficient exposure of the host to the vaccine organism rather than the inability of the host to produce a protective immune response following exposure to the vaccine organism.