Submitted to: Pig Veterinary Society International Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 19, 2004
Publication Date: June 27, 2004
Citation: Stoffregen, W.C., Bricker, B.J., Jensen, A.E., Wheeler, C.J., Olsen, S.C. 2004. Results of a vaccine trial using brucella abortus rb51 in a feral swine herd enzootically infected with brucella in the United States of America. Pig Veterinary Society International Congress Proceedings. Paper No. 717. Technical Abstract: Feral swine serve as reservoirs of both pseudorabies and brucellosis within the US as well as other countries. The transmission of both these diseases from feral swine to domestic livestock has been documented numerous times. Recent attention has been given to determining control strategies for brucellosis within wild swine populations in order to prevent further outbreaks of this disease in domestic livestock and humans. Initial reports suggested some efficacy of the Brucella vaccine B. abortus RB51 in preventing transmission of B. suis in swine (1,2). However, this had never been investigated in an enzootically infected feral pig population. This study was designed to 1) characterize the efficacy of B. abortus RB 51 vaccination to prevent Brucella infection in a feral swine population with a high prevalence of brucellosis; 2) determine if serologic status influences efficacy of RB 51 under field conditions; 3: Determine if feral swine stay persistently infected with RB51 after vaccination; and 4) provide additional serologic and tissue localization data on infection of feral swine with Brucella sp. During the winter of 2001-2002, 244 juvenile and adult feral swine were trapped within a Brucella enzootic 7,100 hectare tract of land on a peninsula between the Atlantic Ocean and the Winyah Bay in Georgetown County, South Carolina. All animals were bled (10 ml for serology), ear-tagged, and implanted with an identification microchip. One-half of the animals were given 1 x 1010 CFU B. abortus RB51 (live vaccine) by IM injection in the right cervical area. Brucella serologic status of all animals was determined by fluorescent polarization, standard tube, and card agglutination assays. Ten to fourteen months after initial capture 80 of the originally captured animals were recaptured, euthanized, and complete necropsies were performed. Blood was taken for serology by the previously listed assays. The following tissues, fluids, and swabs were harvested for bacteriological culture: liver, spleen, lung, kidney, uterus, mammary tissue, testis, seminal vesicle, bulbourethral gland, prostate, urine, blood, nasal swab, vaginal swab, and lymph nodes including prescapular, medial retropharyngeal, sternal, tracheobronchial, gastrohepatic, prefemoral, popliteal, mandibular, and parotid. All tissues were freshly frozen at -70° C. After thawing, tissues were ground in approximately 10% (w/v) sterile PBS and plated on the following media: tryptose agar with 5% bovine serum, Kudzas Morse (KM) agar, and brilliant green agar (BGA). Brucella suspect colonies were picked on the basis of morphologic characteristics and typed as Brucella by a PCR assay which targeted the conserved omp 2a portion of the Brucella genome. PCR positive samples were subcultured onto KM and/or BGA agar for individual colony isolation. Individual colonies were isolated, propagated, and characterized by standard biochemical, antigenic, phage typing, and molecular techniques. Standard identification strategies included growth on selective media, urease characteristics, hydrogen sulfide production, antibiotic sensitivity, phage typing, and major antigenic characterization. Isolates were species typed using several PCR assays. A multiplex PCR assay which could differentiate Brucella abortus, Brucella abortus RB51, and Brucella abortus S19, from other Brucella species was used to screen initial subcultures and in some cases primary isolates. PCR assays against the omp 2a and omp 31 loci combined with RFLP analysis helped species type and subgroup the isolates. Select isolates were also characterized using a newly described variable number tandem repeat (VNTR) assay for Brucella which allowed the identification of genomic similarities and differences among the isolates based on the VNTR polymorphisms. RB 51 had no effect in preventing the transmission of Brucella spp. in this feral swine herd. Vaccinated animals which were initially seronegative had a seroconversion rate of 32.0% as compared to 40.0% among nonvaccinated, seronegative animals. Brucella culture positivity rate was 67.9% among vaccinated animals which were initially seronegative compared to 64.0% for nonvaccinated, seronegative animals. Often both species were cultured from individual animals. RB 51 persisted in 6/42 animals which were vaccinated and recaptured. Both Brucella suis and Brucella abortus were recovered, and multiple subgroups within each species were identified. More detailed results of this study will be presented.