Canine seroprevalence and the distribution of Ixodes dammini in an area of emerging Lyme disease

This study evaluates the relative usefulness of canine serosurveys to predict risk of exposure in an area of emerging Lyme disease by comparing the distribution of canine seroprevalence with that of vector ticks. From 16 veterinary clinics throughout the State of Maine, 828 canine sera were obtained during the heartworm-testing months of April and May 1989 and measured for anti-Borrelia antibodies by enzyme-linked immunosorbent assay. In the same year, 1605 ticks, including 585 Ixodes dammini, were collected from pets, humans, small mammals, and deer. Thirty-six dogs were seropositive, 28 of which had not traveled to endemic areas. Eighty-nine percent of all seropositive dogs were from towns within 20 miles (32 km) of the coast; the great majority lived within 5 miles (8 km) of tidewater (odds ratio = 4.45, P = .002). Positivity varied from 17% in a southern coastal clinic to 0% in four northern clinics. Of 585 I. dammini identified, all but 5 (99.1%) were also from towns within 20 miles of the coast. Comparison of I. dammini submissions with those of another commonly found tick, Ixodes cookei, corroborated this predominantly coastal distribution. Canine seropositivity generally coincided with this coastal range. These data predicted areas of risk for human Lyme disease, although the prevalence of reported cases remained low.