Early detection of Brucella canis via quantitative polymerase chain reaction analysis

Canine brucellosis is a reportable zoonotic disease that can lead to canine reproductive losses and human infection through contact with infected urine or other genitourinary secretions. Although many locations require testing and euthanasia of positive dogs, current diagnosis is limited by the time required for seroconversion, for example, presence of B. canis-specific antibodies. The goal of this study was to determine the diagnostic ability of Brucella canis-specific quantitative polymerase chain reaction (qPCR) assay to detect B. canis in field samples prior to serological positivity for faster diagnosis and prevention of transmission within kennels or in households. Two kennels, one of which was located in the owner's home, were sampled following observation of suggestive clinical signs and positive serology of at least one dog. Specimens obtained were comparatively analysed via serology and qPCR analysis. 107 dogs were analysed for B. canis infection via qPCR: 105 via whole-blood samples, 65 via vaginal swab, six via urine and seven via genitourinary tract tissue taken at necropsy. Forty-five dogs were found to be infected with canine brucellosis via qPCR, of which 22 (48.89%) were seropositive. A statistically significant number (P = 0.0228) of qPCR-positive dogs, 5/25 (20.00%), seroconverted within a 30-day interval after initial serologic testing. As compared to serology, qPCR analysis of DNA from vaginal swabs had a sensitivity of 92.31% and specificity of 51.92%, and qPCR analysis of DNA from whole-blood samples had a sensitivity of 16.67% and specificity of 100%. B. canis outer membrane protein 25 DNA qPCR from non-invasive vaginal swab and urine samples provided early detection of B. canis infection in dogs prior to detection of antibodies. This assay provides a critical tool to decrease zoonotic spread of canine brucellosis, its associated clinical presentation(s), and emotional and economic repercussions.