Resistance may play a small role in efficacy failures, but evidence suggests lack of education is the real reason preventives don't work.
Spring has arrived, and with the change in season come warmer temperatures, a resurgence of blossoming trees and flowers and, for most of us, a general feeling of freedom from the harsh confines of winter. Chances are, the change in season will prompt most veterinary hospitals to revisit parasite prevention protocols that may also have become dormant in the winter months.
"The best method of treatment is prevention." -Chris Carpenter, DVM (GETTY IMAGES/MAARTEN WOUTERS)
But what could be troubling to many practitioners as they gear up to talk to clients about heartworm prevention are reports that preventive products are losing efficacy. According to Tom Nelson, DVM, executive board member and former president of the American Heartworm Society as well as partner at Animal Medical Center in Anniston, Ala., concerns about heartworm resistance and preventive efficacy are nothing new—in fact, they've been going on for about a decade now.
While he agrees that further investigation into these concerns is warranted, Nelson says that in his area of the country—the Deep South, where heartworm disease is prevalent year-round—most of the so-called efficacy issues associated with certain heartworm preventives can be attributed to poor veterinary client compliance.
"Can it be that there are certain heartworm isolates out there with decreased sensitivity to preventives? Yes," Nelson says. "But everything we've found when we've looked at these lack-of-efficacy cases in the Delta area is that 99 percent are compliance problems—gaps in doses and missed doses."
Although it's true that heartworm transmission does decrease in the winter months in many parts of the country, the American Heartworm Society reports that the disease can still be transmitted year-round—even in seemingly less likely areas—thanks to pockets of microenvironments where the right combination of temperature and humidity can sustain a viable mosquito population. But for Nelson and other veterinarians in the southern part of the country, there's no question that the disease can be transmitted year-round—and that appropriate measures should be taken.
The American Heartworm Society recommends annual antigen testing and year-round administration of heartworm preventive for dogs, and although this might seem like an easy protocol to follow, it's actually where control and prevention of heartworm disease break down. "Veterinarians really need to emphasize to pet owners that giving heartworm preventive every month means giving it on the same day every month," Nelson says.
And that means making a point to send reminders to clients for more than just yearly wellness exams, vaccinations and heartworm tests. His advice? Veterinarians need to take it a step further and remind clients when their pet's monthly pill is due. With advancements in technology and the ease of texting and e-mailing these days, there's no excuse not to send electronic reminders each month, Nelson says. "We all want to blame the client for not doing what we tell them to, but we have to take some blame in that we're not properly educating them," he says.
Chris Carpenter, DVM, executive director of the Companion Animal Parasite Council (CAPC), echoes a similar sentiment about the importance of veterinary client education when it comes to parasite prevention and control.
"The best method of treatment is prevention. It's up to us as practitioners to educate our clients on the risks these parasites pose to their pets and their families," Carpenter says.