A retrospective analysis of 1329 dogs that received a fecal examination and whose owners were surveyed about heartworm prevention was conducted. Dogs under 6 months of age (n = 46) were analyzed separately. None of the dogs under 6 months of age receiving monthly heartworm preventive therapy had ascarids or hookworms; among dogs in this age group that received no preventive products, prevalence of ascarids and hookworms was 5.2% and 11.7%, respectively. Only 75.5% of dogs were administered heartworm preventives, with 83.9% of these receiving them year-round and 16.1% seasonally. A small percentage of adult dogs on preventive had positive fecal exams (0.5% to 2.53%) but efficacy for all products fell well within the label claims. There are limitations with using historical data in a study to estimate product efficacy. Owners had to correctly report the brand name, duration of use, and compliance. Veterinary personnel taking the medical history had to record the appropriate information. As the medical coding was the same for a product with a low dose of ivermectin (Heartgard) and a product with ivermectin–pyrantel (Heartgard Plus), it was impossible to differentiate which product had been used. Despite the limitations of the study, it is clear that routine fecal screening should be recommended, even for patients that are on heartworm preventive.

Commentary:
This research strengthens our recommendation for use of broad-spectrum heartworm preventives in dogs for additional control of potentially zoonotic and pathogenic internal parasites. The results substantiate the importance of administering these products to dogs at an early age to prevent both primary disease and soil contamination with eggs of Toxocara canis and Ancylostoma spp. The results seen for Trichuris vulpis, present in all major geographic regions of the U.S., in patients on different products confirm differences in product label claims. The authors conclude that the medication, not the degree of patient care, was responsible for the results seen in patients over 6 months of age. Selection of products, in my opinion, does reflect quality of patient care, as it requires knowledge of regional parasites, accurate and timely conduct of fecal examinations, and subsequent product recommendation. This is why it is important for clients to take their pets to a veterinarian for proper patient examination and appropriate product recommendations. In addition, the dogs in this retrospective study were from the northeastern region of the U.S. Results from regions such as the Southeast could lead to different conclusions for some of the parasites.—Byron L. Blagburn, MS, PhD

Efficacy of heartworm preventatives against ascarids and hookworms in client-owned dogs: A retrospective case control study. Gates MC, Nolan TJ. J VET PHARMACOL THER 34:116-119, 2011.