Dear Ounce: Heartworms are parasitic worms living in the arteries of the lungs and in the right side of the heart, causing a variety of health problems, possibly leading to death. Mosquitoes help spread the disease in a vicious cycle to and from pets. Pets need testing before beginning any preventive treatment.

Historically, heartworm medications have gone through many changes. In the beginning, a drug called Diethylcarbamazine (DEC), available in little white pills would kill the heartworm larvae in one stage of its life, when it was 48 hours old. Dog owners would give this medication on a daily basis (every 24 hours) to make sure the dog had the drug in its system when the larvae reached the age when the medication would kill it.

 These pills evolved into the daily chewable Filarabits® tablets which were very popular for many years. Eventually, chewable tabs given monthly and injections given bi-annually were developed. Today, there are three FDA-approved products for heartworm control in dogs. They are ivermectin (Heartgard®), selamectin (Revolution®) and milbemycin (Interceptor® and Sentinel®). Another drug, moxidectin (ProHeart®), used to be on the market, but was recalled by the FDA recently due to side effects.

Some vets began advocating year-round prevention a while back, but just last week during the American College of Veterinary Internal Medicine Forum in Baltimore, the American Heartworm Society (AHS) announced its “2005 Guidelines for the Diagnosis, Prevention and Management of Heartworm Infection in Dogs.”

New Guidelines

The new guidelines are based upon the latest, ongoing research by several sources around the world. The AHS compiles the research to create the guidelines. These sources include pharmaceutical companies, private laboratories and veterinarians and parasitologists at several universities. These guidelines also address why the extra parasite control is a good idea.

Annual Testing is Necessary – In the past, if a dog had been on preventive methods routinely, it was not necessary to test every year, perhaps only every two to three years. But because of some concerns with breaks regarding animals on preventives that still contracted heartworms the AHS recommends a more conservative testing routine. It may be too difficult to document when an animal hasn’t been checked in three years, and therefore, annual testing will ensure that an infection is caught in plenty of time to effectively manage it.

Switching Prevention Methods Requires Additional Testing – Pet owners sometimes switch between prevention medications, for any number of reasons. In these instances, there are specific time periods to retest in order to ensure the pet is protected. When switching from one product to another, it is necessary to test more often.

Year-Round Prevention is Supported – Most eterinarians recommend year-round heartworm prevention, even in seasonal areas. One reason for this is compliance: making sure the medicine has been given properly by the pet owner. Surveys show that probably only 75 percent of the prescribed doses are given. But, even if doses are accidentally skipped, the drug is still beneficial to the pet. If given consistently over a 12-month period, it’s possible to actually stop worms from developing into adults. Also, monthly heartworm preventives have activity against intestinal parasites, which inadvertently infect three to six million people every year. These preventives protect pets and people. The guidelines are posted on the AHS’s web site at www.heartwormsociety.org.

Lisa’s Pick of the Litter

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Lisa Peterson, a long-time breeder of Norwegian Elkhounds, is the Director of Club Communications at the American Kennel Club. Contact her at ask@lisa-peterson.com or Dogma Publishing, P.O. Box 307, Newtown, CT 06470.