Evidence for unapparent Brucella canis infections among adults with occupational exposure to dogs

Human serological assays designed to detect brucellosis will miss infections caused by Brucella canis, and low levels of periodic bacteremia limit diagnosis by blood culture. Recent B. canis outbreaks in dogs and concomitant illnesses in caretakers suggest that unapparent human infections may be occurring. With more than a quarter of a million persons in occupations involving dogs, and nearly 80 million dog owners in the United States, this pathogen is an under-recognized human health threat. To investigate occupational exposure to B. canis, we adapted a commercial canine serological assay and present the first controlled seroepidemiological study of human B. canis infections in recent years. 306 adults with occupational exposure to dogs and 101 non-matched, non-canine-exposed subjects were enrolled. Antibodies were detected using the canine D-Tec(®) CB rapid slide agglutination test (RSAT) kit with a secondary 2-mercaptoethanol (ME)-RSAT. Results were validated on a blinded subset of sera with an additional RSAT and indirect enzyme-linked immunoassay at the National Administration of Laboratories and Health Institutes (ANLIS) in Argentina. Seroprevalence ranged from 10.8% (RSAT) to 3.6% (ME-RSAT) among canine-exposed subjects. Kennel employees were more likely to test RSAT seropositive compared with other canine exposures (OR = 2.7; 95% CI, 1.3-5.8); however, low seroprevalence limited meaningful occupational risk factor analyses. Two seropositive participants reported experiencing symptoms consistent with brucellosis and having exposure to B. canis-infected dogs; however, temporality of symptom onset with reported exposure could not be determined. D-Tec(®) CB results had substantial agreement with ANLIS assays (Cohen’s kappa = 0.60-0.68). These data add to a growing body of literature suggesting that people occupationally exposed to dogs may be at risk of unapparent B. canis infection. It seems prudent to consider B. canis as an occupational public health concern and encourage the development of serological assays to detect human B. canis infections.