New Buzz on Heartworm Prevention

By Steve Dale

New guidelines for heartworm prevention developed by the American Heartworm Society are being announced this week in Baltimore, MD at the 2005 Forum of the American College of Veterinary Internal Medicine. This is the annual meeting of the organization for veterinary medicine specialists in neurology, oncology, cardiology and internal medicine.

            One change in the Heartworm Society guidelines is that all dogs are now encouraged to be tested for heartworm annually.

            Since heartworm disease is transmitted by mosquitoes, people in communities in warm climates – where mosquitoes buzz year-round – were presumably giving their pups a preventative year-round. Testing to determine if a dog had the disease seemed unnecessary since the preventatives do work. Or at least that’s what everyone thought.

            Dr, Thomas Nelson, president of the American Heartworm Society, notes that the presumption that clients were giving their dogs the medication year-round might not have been correct. People sometimes forget to use the product, giving the potentially fatal disease a window of opportunity.

            Veterinary parisitologist Dr. Jorge Guerrero, chair of the American Heartworm Society’s Scientific Program Committee says, “When my dog visits my daughter God knows if she follows my instructions and gives the dog preventative. I know many practitioners who give, say six months of a preventative to a client. But then the client doesn’t (seem to) need an additional re-fill for eight months. That means the client forgot to dose the dog two months.”

            The U.S. Food and Drug Administration has received complaints from the general public that some of the products may not be working to prevent heartworm disease. Scientific studies demonstrate the products are indeed effective. So, what’s going on?

            Guerrero, who is an adjunct professor at the University of Pennsylvania School of Veterinary Medicine says while it’s possible mosquitoes (actually the heartworm parasite) have built some resistance, he personally feels that’s unlikely. He says it’s far more probable that people aren’t being fully compliant, missing doses. Indeed previous studies confirm this. According to a 2001 Gallop Poll of 18,000 veterinary clinics around the country, 20 per cent of dog owners forgot to give their pooch at least one dose of the monthly preventative and some stopped all together for several consecutive months.

            Still, before jumping to any conclusions, the FDA and the Heartworm Society require further data, and more efficient tracking of what the public is doing.

            Nelson says that the FDA has suggested more frequent testing. It’s a plan that he believes makes sense, although clients will, of course, have to pay for that annual heartworm test. He says, “By testing annually we can better track of which clients are doing what. We’ll have a handle on if the client is skipping months. Or if a client switches the heartworm preventative (from using one brand to another brand), we’ll know it.”

            Nelson, who is based in Anniston, AL, believes annual testing of all dogs is a canine public health issue. Also, it’s better medicine. Since some of the preventatives seem to also have the additional ability to fight off the disease, heartworm disease may go undiagnosed in some dogs. For example, if the clients forgot to dose the dog for two months – the heartworm disease takes hold, and then without knowing the dog is sick, the owner continues the preventative again on a monthly schedule.

Of course, dogs do have a better chance to survive if the veterinarian is able to understand the dog has heartworm, and therefore offer appropriate medical advice. For example, one recent Italian study revealed the more active the dogs with heartworm are, the worse their lungs may get. Veterinarians now suggest restricting exercise for dogs with heartworm disease

            Heartworm is a miniscule parasite transmitted through the mouth parts of infected mosquitoes. Once settling inside a dog, the parasite evolves into a six to 12-inch long spaghetti shaped worm winding around the arteries and perhaps settling in the lungs. Unprotected dogs may have dozens of these worms, or even over 100. It’s no wonder the dog’s health is impacted. Effects may include coughing, intolerance to exercise and potentially congestive heart failure.

            Another change in the guidelines is a new recommendation to use a preventative year-round, even where mosquitoes aren’t prevalent for all 12 months.

Nelson says if say in Detroit a client hasn’t used a preventative in the winter months, and then the dog throws up the preventive pill given in May without the owner realizing it, that dog could easily wind up with heartworm disease. However, if you’re using a preventative year-round, and the dog throws up a pill in May, there’s considerable left over protection from all the other months the dog is treated with the preventative.

            Also, many of the heartworm preventatives double as protection against internal parasites, such as hookworm and roundworm. In many parts of the country, these internal parasites are a major concern, particularly roundworm because of its potential to be transmitted to people.

            The American Heartworm Society is also now strongly encouraging preventatives for cats.” I have no doubt that heartworm disease in cats is under-diagnosed,” says Nelson. New research demonstrates that at least some cats diagnosed with feline asthma in actuality have feline heartworm disease.

            Sadly, often the only symptom of heartworm in cats is sudden death. “No one knows exactly how often that happens,” says Nelson. “Usually the owners just quietly bury their cat, and never report it to the vet. Or if they do, it’s unlikely they’ll want a necropsy (an animal autopsy) to confirm the cause of death (there are several possible explanations for sudden death in cats).”

            “We’re working in Spain and in Italy to find ways to more efficiently detect heartworm in cats,” adds Guerrero. “And there is no treatment. However, heartworm can be prevented. When the possible outcome is death (in cats and dogs) certainly it seems logical to use the preventative.”

            Learn more at www.heartwormsociety.org.