Canine brucellosis: serologically diagnosed positive cases

Canine brucellosis is a devastating disease as it carries zoonotic potential and there are no effective treatments to clear infections in affected animals. Thus, animals that test positive are commonly euthanized. It is thought to primarily affect intact animals and can be readily transmitted through oral or venereal route. In past few years, number of inquiries for advice on managing positive animals has increased sharply. Goal was to evaluate serologically positive Brucella canis submissions. We hypothesized that number and proportion of positive cases would vary by year, source of submission, and patient demographics. Results from samples submitted for B. canis slide/Agar Gel Immunodiffusion (AGID II) tests to Cornell Animal Health Diagnostic Center from 2014 - 2019 from US were included in this retrospective study. Submissions were classified as either from a referral laboratory or from a veterinarian. Patient demographics (age, breed, and gender), source (referral laboratory or veterinarian, and state/region), and year were evaluated for association with positive serological diagnosis using logistic regression analysis SAS (v9.4) proc logistic. All variables tested were associated with positive serology (p < 0.0001) and were retained in final model. Number and proportion of positive cases were: 231 (16.8%) in 2014, 199 (10.3%) in 2015, 232 (11.4%) in 2016, 217 (11.8%) in 2017, 414 (14.8%) in 2018, and 293 (10.0%) in 2019. Referral laboratory submissions (n = 882; 17.4%) had more positive submissions compared to veterinarian submissions (n = 704; 9.0%). Animals between 1 - 6 years of age and mix breeds were more likely to be serologically positive compared to pure breeds. Most (83.0%) submissions were from intact animals, but proportion of positive animals was higher in spayed (33%) versus intact females (9%) and castrated (28%) versus intact males (8%). Number and proportion of serologically positive submissions were significantly different among South (14%), West (12%), Midwest (9%), and Northeast (3%) regions. Many submissions were likely prescreened by card agglutination test; thus, results should be interpreted with this in mind. Years 2018 and 2019 had higher number of positive submissions compared to 2014 - 2017. Submissions from young, mixed-breed animals were more likely to test positive, and intact animals had higher numbers but lower proportions of positive cases. Regional difference was also observed. We recommend testing breeding animals and semen to reduce spread of disease.

Keywords: Canine brucellosis, AGID II test

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.