Preventing heartworm in dogs


A friend who fosters dogs before they are adopted recently lost one to heartworms. While that was sad, it was also maddening, because heartworms are nearly preventable, if their presence inside the canine’s heart is detected early enough. When it is discovered that they have infected the dog, it is too late–treatments can be expensive, hard on the dog and not guaranteed to work.

In the case of the friend’s dog, the best remedy was euthanasia.

For man’s best friend, heartworm can be one of the most dangerous diseases they can develop. Once it is detected, it is already inside the dog. Before modern medications were developed to treat heartworm, it used to be considered a death sentence for the dog. Up until the 1980s, in fact, the only treatment available was an arsenic derivative, so while veterinarians were trying to kill the worms, sometimes they killed the dog as well.

Starts as a parasite

Heartworm, which is caused by a parasite, can be traced to the bite of a mosquito. The life cycle of a heartworm begins when a mosquito bites a dog already infected with heartworms and ingests the earliest stage in the life of the pest. For 10 to 30 days, the nascent worms develop in the mosquito’s gut and then move on to the insect’s mouth.

When the mosquito bites another dog, it releases the larvae into the dog, where they migrate to the bloodstream and move into the heart and blood vessels, maturing, mating and reproducing, all within six to seven months. It is not a pleasant thought, but heartworms can grow up to 14 inches long and live up to seven years inside a dog.

However, because of the time it takes for heartworm to develop, it is not found in puppies. As a result, they are the best patients for preventive treatment.

Some symptoms of heartworm infection are:

  • Chronic coughing
  • Difficulty breathing
  • Fatigue
  • Loss of appetite
  • Rough hair coat
  • Fainting

As heartworms grow and multiply, your dog will become winded as he walks and his heart rate will increase. The heart will become enlarged and cardiac failure could result.

Entirely preventable

While they sound, and are, disgusting, heartworms, and the pain they cause canines, can be prevented. Keeping mosquitoes out of the house and yard sounds reasonable, but it is difficult. Once your dog is outside–because dogs should spend time outdoors–the mosquito can have at it. That is when preventive medications do their work.

Before he/she administers a preventive, the vet will take a blood sample for testing to see if the dog is already infected. If heartworms are detected, the vet will take a more aggressive approach at treating the dog, with no guarantees that it will work.

Prevention options are not nearly as draconian. Dog owners can opt for daily and monthly tablets and chewables and/or monthly topical treatments. Injections provide protection for up to six months and are the better choice if the dog vomits the tablets or shuns eating them.

Only one bite

These vaccinations contain drugs that destroy the heartworm larvae before they mature, mate and create more of the parasite. In areas of the country where temperatures plummet in the late fall, the dog will be given the preventive only in spring, summer and fall. If the dog resides in the more temperate parts of the country, the preventive will be given year-round. Remember, it only takes one bite from an infected mosquito to transmit the parasite to your dog.

Unfortunately for the friend’s foster dog, he was already infected with heartworms when he was rescued from a previous, negligent owner. The veterinarian administered the more potent treatment, which is also more expensive, killing the worms, which became deadly blood clots. Those were ultimately impossible to treat. That is an extreme case–with a caring owner and regular vet visits, heartworms are easily preventable. Fido will be forever grateful.


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