Elevated Lyme disease seroprevalence among dogs in a nonendemic county: harbinger or artifact?

Lyme disease, a tick-borne illness caused by Borrelia burgdorferi, infects humans and other species, including dogs. Canine seroprevalence has been suggested as a sentinel marker of human disease risk. A recent publication reported high canine seroprevalence (>5%) in Routt County, Colorado, an area where Lyme disease is generally considered nonendemic. We surveyed veterinarians in Routt County and discovered that 11 of 12 seropositive dogs (>90%) had a documented history of travel to or residence in a Lyme disease endemic area. These findings do not support the presence of an undocumented disease focus and reveal that despite its high sensitivity, there are limitations in the specificity and positive predictive value of elevated canine seroprevalence as a marker of human risk.