Seroprevalence of canine brucellosis in the southeastern United States

There are four Brucella strains of zoonotic importance: smooth strains, i.e. Brucella abortus (B. abortus), B. melitensis, B. suis, and a rough strain, i.e. B. canis. Dogs can serve as hosts for all four zoonotic strains; however, standard serologic testing in dogs is limited to the identification of only B. canis antibodies. Well known to be transmitted venereally, Brucella are also readily shed in urine, feces, saliva, milk, and respiratory secretions, and can be easily transmitted through close contact. There is no approved treatment for the elimination of Brucella from infected animals. Human infection is a nationally notifiable condition, as treatment is not always effective in clearing the organism, resulting in recurrent infection. Therefore, preventing spread of disease is paramount for public health. The goal of this pilot study was to estimate the number of dogs with circulating antibodies to any of the four zoonotic strains of Brucella by sampling multiple subpopulations of hog hunting dogs, dogs presenting for routine spay and neuter, and imported animals throughout the southeastern United States. We hypothesized that the seroprevalence of smooth strains of brucellosis would be higher in imported and hog-hunting dog populations than dogs presenting for routine spay and neuter, and that the seroprevalence of the rough strain of brucellosis (B. canis) would be similar across all groups. To date, serum has been harvested from 65 client owned dogs (30 hog hunting and 35 companion dogs) and 19 shelter owned dogs of various ages, parities, and breeds. Reproductive tissues, semen and/or vaginal swabs were collected when available. Brucellosis serology was performed using the Canine Brucella Slide Agglutination test (SAT), Brucella canis Agar Gel Immunodiffusion II test (AGID), Brucella abortus Card Agglutination test (CAG), and Brucella abortus Fluorescence Polarization Assay (FPA). To date, among 84 samples collected and assayed, one shelter dog tested positive for a rough Brucella strain via AGID. An imported dog tested positive for both a rough and a smooth strain of brucellosis via SAT, AGID and FPA, and two client owned dogs tested positive for a smooth Brucella strain by a National Veterinary Services accredited laboratory via B. abortus plate and card agglutination. Three attempts at culturing the organism from reproductive tissue samples of seropositive animals yielded contaminant growth only. All other samples (n = 80) were seronegative. Although this project is still ongoing, at this time, 4 of 84 samples (5%) tested positive for at least one strain of Brucella, with 3 of 4 positive samples (75%) testing positive for a smooth Brucella strain. All hog-hunting dogs sampled were seronegative. Our preliminary results support an overall low seroprevalence rate for brucellosis, with most samples testing positive for a smooth Brucella strain, thus, supporting the need for a commercially available, validated test for the smooth strains in canines. To the authors’ knowledge, this is the first study evaluating the seroprevalence of the smooth strains of brucellosis in dogs in the US.

Keywords: Canine brucellosis, rough strains, smooth strains, seroprevalence

This manuscript was originally published in the journal Clinical Theriogenology Vol 12(3) Sept 2020.  Clinical Theriogenology is the official journal of the Society for Theriogenology (SFT) and the American College of Theriogenologists (ACT).  This content has been reproduced on the IVIS website with the explicit permission of the SFT/ACT.