Declines in canine endoparasite prevalence associated with the introduction of commercial heartworm and flea preventatives from 1984 to 2007

The apparent monthly prevalence of endoparasite infections was measured from 20,991 dogs that had fecal examinations performed upon presentation to the Veterinary Hospital of the University of Pennsylvania between 1984 and 2007. In the period from 1984 to 1991, the mean monthly prevalence of endoparasites was 5.32% for ascarids, 9.80% for hookworms, 9.64% for whipworms, 1.84% for tapeworms (Dipylidium caninum), 4.59% for Giardia species, and 3.04% for coccidia. Based on Student's t tests, the prevalence of ascarids (1.99%), hookworms (1.48%), whipworms (2.33%), and tapeworms (0.29%) were found to be significantly lower in the period from 2000 to 2007. Plots of the smoothed monthly averages revealed that the declines in prevalence occurred shortly after the introduction of modern heartworm and flea preventatives to the commercial market. In the latter study period, 79.8% of dogs were on monthly heartworm prevention and 74.0% were on monthly flea prevention. There were no significant differences in the prevalence of either Giardia species or coccidia species between study time periods. Overall, the findings suggest that heartworm and flea preventatives have had cascade effects on endoparasite prevalence in the population of well-cared-for dogs.