Diagnostic Characterization of a Feral Swine Herd Enzootically Infected withBrucella

Abstract

Abstract. Eighty feral swine were trapped from a herd that 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.

Immunogenicity and Efficacy of a Rough Brucella suisVaccine Delivered Orally or Parenterally to Feral Swine

“…Virulence of this strain was also supported by data obtained in previous studies in which in vivo persistence of this strain after conjunctival inoculation was characterized in naïve pigs (Olsen, unpublished). The observed high rate of infection in non-vaccinated swine after experimental infection in the current study was similar to the prevalence of Brucella infection in feral swine under field conditions [23]. In that study, the high recovery rate (77.5%) of Brucella in randomly trapped feral swine most likely reflects the epidemiologic features of brucellosis in a chronically infected feral swine population.…”

Brucellosis at the animal/ecosystem/human interface at the beginning of the 21st century

“…Infections with B. suis in humans occur in people handling pigs on farms and during slaughtering and processing, including the hunting of feral swine. Recently, it has been shown in South Carolina, USA, that feral pigs were infected with B. abortus wildtype, S19 and RB51 vaccine strains besides B. suis biovar 1 (Stoffregen et al, 2007). The importance of this finding lies in that pigs were for the first time demonstrated to act as reservoir host of B. abortus in the absence of contact with cattle for more than 25 years.…”

The quest for a true One Health perspective of brucellosis

“…It should be noted that maintenance of B. abortus has also been documented in feral swine, including feral swine that had been spatially separated from domestic livestock for decades (24). The epidemiological consequences of these findings are important.…”

“…-silent transmission in marine wildlife reservoirs, with no or minimal signs of the disease in animals which coevolved with the bacterium, and with fish or invertebrates as a possible source of infection (67) -spillover from terrestrial wildlife reservoirs to livestock and thence to humans (6) -persistence in soil (68,69) -active transmission to rodents (70) or potentially to coldblooded hosts (71 (24). The changing epidemiology of brucellosis is described below.…”