Heartworm infection in domestic dogs in Canada, 1977-2016: Prevalence, time trend, and efficacy of prophylaxis.

Dirofilaria immitis (heartworm) is a mosquito-borne parasite that primarily infects domestic and wild canids. The objectives of this study were to i) determine if there has been a temporal change in prevalence of heartworm infection among domestic dogs in Canada from 1977 to 2016; ii) explore the spatial extension of heartworm across Canada using choropleth maps; and iii) assess the efficacy of preventive drugs using the estimated "Attributable Fraction Exposed." Heartworm surveys that collected data from 1977 to 2010 and serological laboratory data from 2007 to 2016 were analyzed. The data depicted a decrease in heartworm prevalence, both nationally and provincially, from 1977 to the early 2000s. However, an increase in prevalence was identified for tested dog populations in Manitoba and Quebec from 2007 to 2016. Chemoprophylaxis was associated with an estimated 93.0% [95% confidence interval (CI): 92.85, 93.3] reduction of heartworm infections in domestic dogs in Canada from 1977 to 2010.