Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2007
Publication Date: 5/1/2007
Citation: Stoffregen, W.C., Olsen, S.C., Wheeler, C.J., Bricker, B.J., Palmer, M.V., Jensen, A.E., Halling, S.M., Alt, D.P. 2007. Diagnostic Characterization of a Feral Swine Herd Enzootically Infected with Brucella. Journal of Veterinary Diagnostic Investigation. 19(3):227-237. Interpretive Summary: Swine brucellosis is a bacterial disease caused by Brucella suis which causes abortions and chronic infections of multiple organs. The bacteria which cause brucellosis in swine are also capable of infecting humans who have contact with infected swine or swine products from infected animals. Infected feral swine may also serve as a reservoir of infection for domestic livestock. The current paper characterizes Brucella infection in a feral swine herd. The work reported within this paper found that this feral swine herd was not only infected with Brucella suis but also Brucella abortus. Prior to this report, it was thought that the only reservoir of Brucella abortus infection in the United States was within elk and bison populations in the Greater Yellowstone Area of Wyoming, Montana, and Idaho. This paper also characterized lesions found within this feral swine herd which could be associated with the Brucella infection. The paper also shows that standard serologic diagnostic techniques are not highly sensitive to diagnose brucellosis in chronically infected swine.
Technical Abstract: Eighty feral swine were trapped from a herd which had been documented to be seropositive for Brucella and which had been used for Brucella abortus RB51 vaccine trials on a 7,100 hectare tract of land in South Carolina. The animals were euthanized and complete necropsies were performed. Samples were taken for histopathology, Brucella culture, and Brucella serology. Brucella was cultured from 62 (77.5%) animals. Brucella suis was isolated from 55 animals (68.8%), and all isolates were biovar 1. Brucella abortus was isolated from 28 animals (35.0%), and isolates included field strain biovar 1 (21 animals; 26.3%), vaccine strain Brucella abortus S19 (8 animals, 10.0%), and vaccine strain Brucella abortus RB51 (6 animals, 7.5%). Males were significantly more likely to be culture positive than females (92.9% vs. 60.6%). Thirty-nine animals (48.8%) were seropositive. Males also had a significantly higher seropositivity rate than females (61.9% vs. 34.2%). The relative sensitivity rates were significantly higher for the standard tube test (44.6%) and fluorescence polarization assay (42.6%) than the card agglutination test (13.1%). Lesions consistent with Brucella infection were commonly found in the animals surveyed and included inflammatory lesions of the lymph nodes, liver, kidney, and male reproductive organs which ranged from lymphoplasmacytic to pyogranulomatous with necrosis. This is the first report of an apparent enzootic Brucella abortus infection in a feral swine herd suggesting that feral swine may serve as a reservoir of infection for Brucella abortus as well as Brucella suis for domestic livestock.