Heartworm disease, heartworm tests, heartworm preventative – your animal’s yearly wellness exam always has some mention of heartworms. But what are they and why should you be concerned?

Heartworms, or Dirofilaria immitis, are a very common parasite. Their primary host is the dog, but they can occasionally infect a variety of mammals including coyotes, ferrets and cats. The vector, the creature that transfers this parasite, is the mosquito.

The mosquito bites an animal that has immature heartworms circulating in its bloodstream, and ingests them. After several days, the mosquito bites another unsuspecting animal, injecting a larval stage under the skin. It takes six or seven months of traveling through the body, and continued maturation, but eventually this parasite arrives in the animal’s heart and sets up shop. These worms can live for up to seven years in a dog’s heart.

Studies have shown that dogs can have anywhere from one to 250+ heartworms living in their hearts. Male worms are usually about 6 inches long; females twice that. It doesn’t take much imagination to figure out how much damage hundreds of foot-long worms can cause in an average dog’s heart.

According to the American Heartworm Society (a society of veterinary researchers, not worms!), the highest rate of heartworm-infected dogs is within 150 miles of the Atlantic and Gulf coasts, from the Southeast to New Jersey. In addition, the Mississippi River and its tributaries have extremely high rates of infection. It makes sense; these areas are peak mosquito country. Georgia lies smack in the middle of it all. And research shows that 45 percent of dogs not on heartworm preventative in this region will get heartworms.

Heartworms can cause a variety of symptoms in your dog. In the early stages, you may not see anything. Later you may notice a worsening cough, or your pet tiring with relatively little exercise. As the worms continue to irritate the pulmonary veins, grow and eventually all but clog the heart chambers, the dog will experience heart failure. Occasionally, with advanced disease, we see collapse and sudden death.

Heartworm disease can be treated, although the better strategy is to prevent it. In Georgia, heartworm preventative should be given monthly, all year. It comes in numerous convenient forms: an unflavored tablet for those with food allergies, a tasty treat for those hard to pill, or topical medication for owners who want to combine heartworm preventative with flea control. Quite frankly, I don’t care which of the products my owners use – as long as they use one and use it consistently.

These heartworm preventatives are very effective, but not 100 percent. That is why every dog should be tested for heartworms yearly. In my practice, we see several dogs a year who, according to the owner, have been on preventative, but still test positive. We never know if the owner forgot, if the dog spit it out behind the couch, or if this is truly a case of parasite resistance.  What we do know is that if we find an infection early, it is almost always treatable.

In Georgia, your dog needs to be tested yearly and stay on heartworm preventative – period. And cat owners, stay tuned – we’ll talk about your pets next month.