Everything You Need to Know About Heartworm

A sad dog leaning against the couch.

April is Heartworm Awareness Month. If you have a cat or dog, you probably know that heartworm is a parasite your pet can get and that preventive medication is almost always needed. But what exactly is heartworm, and what happens if your pet gets it? 

What is Heartworm?

Heartworm disease is a potentially deadly condition caused by the parasitic worm, Dirofilaria immitis. Dogs are one of the parasite’s natural hosts, unfortunately. When a dog is infected with the parasite, adult female heartworms spawn offspring called microfilariae. The microfilariae spread through the dog’s bloodstream. When another mosquito bites the dog, the insect becomes infected, too—and its tiny body is the only place where microfilariae can turn into infective larvae.

The microfilariae will spend two weeks inside the mosquito becoming larvae. The mosquito will inevitably bite another dog after this, spreading the larvae into the dog’s bloodstream and starting the cycle all over again. Within six or seven months, the larvae will mature into adult heartworms. 

These adults measure between 4 and 12 inches long and look like spaghetti noodles. They live in the pet’s heart, lungs, and blood vessels, causing heart failure, organ damage, and lung disease. Even worse, they’ll typically stay alive—and keep reproducing—inside a dog for 5-7 years, or for 2-4 years in a cat. 

Dogs often end up hosting about 15 worms. However, the numbers can soar into the hundreds. Cats, on the other hand, aren’t natural heartworm hosts. They usually live with one or two worms, which is still a lot for their smaller bodies to deal with.

Signs of Heartworm in Dogs and Cats

In the early stages of heartworm disease, dogs and cats may show few or no signs of infection. However, the disease will get worse as the worms grow and multiply. There are four stages of heartworm disease: 

  • Class 1: An infrequent cough or no symptoms at all.
  • Class 2: Mild or moderate symptoms, including fatigue after going for a walk or playing outside.
  • Class 3: Symptoms become more intense and may include a nagging cough, tiredness after any activity, difficulty breathing, loss of appetite, and signs of heart failure. Cats may vomit blood and/or food. 
  • Class 4: Also known as caval syndrome, Class 4 heartworm disease means there’s a large mass of worms blocking the blood flow to the pet’s heart. Many animals with caval syndrome die even with emergency surgery. 

If your cat or dog shows any symptoms of heartworm disease, contact our veterinary team as soon as possible. We can perform blood tests and X-rays to see if your pet has been infected. Heartworm treatment is available for dogs, but it’s hard on your furry friend’s body. The only treatment option for cats is to surgically remove the heartworms. 

Treating heartworm disease after your dog or cat contracts it is costly, risky, and complicated. That’s why the best treatment for this disease is heartworm prevention

How to Prevent Heartworm 

Preventing heartworm is as easy as bringing your pet in to see us for heartworm screening and prevention. Our veterinary team can prescribe a variety of preventive heartworm medications for your pet. We recommend beginning this preventive care when your dog or cat is six to eight weeks old. 

We also recommend a heartworm screening at six months of age, followed by screenings every 12 months after that. If you adopt a dog past the puppy stages, bring them in for a heartworm screening. If you want to learn more about heartworm prevention, give our team a call  or request an appointment online.