Heartworm disease is a parasitic infection transmitted from animal to animal through the mosquito. It affects primarily dogs, but many wild animals--foxes, wolves, coyotes, to name a few-- also carry the disease. Over the past decade we have also started recognizing this disease in household cats. Heartworm disease should not be confused with the much milder intestinal worm condition. Dogs infected with heartworms may cough and become exercise intolerant as the parasites affect the cardiovascular system. Irreversible damage and sudden death may result. Feline Heartworm Disease varies greatly from Canine Heartworm Disease. The feline form is much harder to diagnose, and involves the pulmonary arteries instead of the heart. Though adult worms last only two years in cats versus five to six years in dogs, cats can die acutely from a thrombo-embolism.
The good news is that it is nearly 100% preventable!

Screening and prevention for dogs:

When we test for the disease we look for the presence of heartworm antigens in the pet's blood. It takes approximately 6 to 8 months from the bite of a mosquito for the heartworm to grow to the stage that we can detect them. If a dog has heartworm larvae (baby worms) circulating in his blood and is put on a preventive, serious complications and even death can result. This is why we allow only pups less than 6 months of age to be placed on the preventative without prior testing. Those pups must be tested at the time of their first booster vaccination (approximately 16 months).

There are several types of prevention available: we offer monthly oral prevention (Interceptor® or Sentinel®) and monthly topical prevention (Revolution®). They are different drugs and prevent the disease in different ways. Monthly medication should be given on the same day of each month.

Our recommendations for dogs:

1. All dogs, inside and outside, should be on preventative starting as early as 4 months of age.
2. Pups less than 6 months of age can be placed on the preventative without prior testing. These dogs should be tested at 16 months and every 3 years thereafter.
3. All dogs over 6 months of age should be tested the day prevention is started and every three years thereafter.
4. We cannot legally dispense heartworm preventives to an animal that we haven't examined and/or tested for heartworm disease.
5. If the dog on monthly preventive misses more than 2 weeks of medication, we need to start on preventive and retest again in 6 months for total safety. If the lapse is less than 2 weeks, the preventive can be restarted without additional testing.

Like most diseases, it is both safer and cheaper to prevent heartworm disease than to treat it. Heartworm disease is not at all like intestinal worms. The diagnosis, staging and treatment can cost from $300 to $1200, and has resulted in death in rare cases. So prevention is the key.

Screening and prevention for cats:

The diagnosis and treatment of heartworm disease in cats is very challenging. Screening tests used for dogs are not always sensitive enough to detect the infection in cats. Also, because we are not able to use the standard drugs used in dogs, currently our only treatment for infected cats is strict rest. Since the adult heartworms can live up to two years, the rest period must last for two years.

Prevention of the disease, as is usually the case, is a simpler and less expensive alternative. We currently recommend Revolution® for heartworm prevention in cats. It is a topical medication which is applied monthly to the back of the cat's head, and has the added advantage of controlling fleas and earmites as well as heartworm. Heartworm preventive labeled for dogs cannot be used for cats.

Our recommendations for cats:

1. Due to the severe nature of the disease we recommend that all cats be on a heartworm preventive. Studies have shown that indoor cats have a higher risk of contracting this disease if bitten by an infected mosquito.
2. Prevention can start as early as eight weeks of age. There is currently no effective test for feline heartworm; we suggest simply placing your cat on the monthly preventive.
3. We cannot legally dispense heartworm preventives to an animal that we have not examined in the last twelve months.