The Case for Year-Round Parasite Controlby Dwight D. Bowman, MS, PhD College of Veterinary Medicine, Cornell University, Ithaca, N.Y.
What’s an acceptable number of canine heartworm cases in the United States?
Once, heartworm disease was confined to the lower reaches of the Mississippi River and coastal areas of the southeastern United States. Today, autochthonous transmission of heartworm has been confirmed in all 50 states and throughout Canada, and nearly 250,000 dogs are treated each year for heartworm infections.
Yet heartworm has been 100 percent preventable for decades. For 20 years, we’ve had access to products that are 100 percent efficacious in preventing the disease when used as directed. Furthermore, many of today’s preventives have a spectrum of activity that also prevents dogs from becoming infected with other common canine parasites. These products are easy to administer either orally, topically or by injection. The products are competitively priced, and clients can be guaranteed their dogs will be protected from heartworm disease for about $120 per year.
The system isn’t working
The system currently being used to prevent heartworm disease is not working. There are several reasons behind this failure.
Compliance is a significant problem. A study published in the 1999 proceedings of the American Heartworm Society showed that of dogs visiting 36 veterinary clinics, only 48 percent were successfully placed on a heartworm preventive program. And only 75 percent of the treated dogs received the full dose recommended by veterinarians.
Pet owners commonly relocate from area to area throughout the country. Not all dogs in any given region receive adequate veterinary care. And often, veterinarians have been reluctant to start patients on heartworm preventives when the prevalence in the area is low or nonexistent.
Many pets now travel with their owners, exposing them to new parasite risks. A 2001 American Animal Hospital Association survey found that 68 percent of dog owners vacation with their pets. And not all owners consistently keep their pets on a preventive regimen.
Furthermore, veterinary practitioners get mixed messages. Some experts contend heartworm prevention is needed for only six months each year in much of the United States, and for only three months in the northern states and Canada.
Year-round prevention makes sense
I contend that given the dramatic spread of heartworm disease, we should be prescribing year-round prevention. This belief is shared by my fellow members of the Companion Animal Parasite Council (CAPC), the group formed to promote animal and human health through recommendations for diagnosis, treatment, prevention and control of parasitic infections.
Our case for year-round prevention is strong. Available drugs are remarkably safe and have already been tested by the FDA as though they will be given on a year-round basis. There is no reason for the spring madness associated with the beginning of what’s commonly called “heartworm season” in so many veterinary practices. This madness actually is a holdover from the days when diethylcarbamazine was the only heartworm preventive. It had to be given daily and was dangerous to give to a dog with an active infection with circulating microfilariae.
In fact, heartworm prevention should be built into a lifelong pet wellness and prevention program associated with annual or biannual hospital visits, not with seasonality of parasitic disease.
Building heartworm prevention into a year-round program also provides better prevention for various zoonotic agents, including Toxocara canis and Ancylostoma braziliense, that threaten the health of pets and their owners. Many of these parasites can be prevented easily since they can be targeted at the same time as heartworm infection. Ectoparasiticide control also can be built into programs to provide protection of pets and their owners from fleas and ticks.
The time is right
The fact that 250,000 dogs become infected with heartworms each year indicates we are not doing all that should be done. Dogs suffer tremendously from heartworm disease, and their human families suffer emotionally and financially as well.
Studying the historic spread of heartworm infection shows we cannot wait until it appears in an area to initiate preventive therapy. Every three years, the American Heartworm Society publishes maps showing the spread of the disease. And every three years, the maps show greater incidence.
Enough is enough.
We have excellent, safe and effective preventive products. We have a public sufficiently concerned about West Nile virus to again support the mosquito-control infrastructure. And if we act, we can begin to drive heartworm out of the United States. That’s why I believe we should do everything possible to get every dog on year-round prevention.
What’s an acceptable number of canine heartworm cases in the United States? The answer is none.
The time is right to make a difference.