fbpx Skip to Content

How Do Dogs Get Heartworm Disease?

How Do Dogs Get Heartworm Disease?

As annoying as a mosquito bites can be for humans, they can be deadly for our furry companions. Mosquitoes spread a parasitic worm that causes a condition also known as heartworms. That is a serious disease that can result in heart failure, lung disease, and death. But how do dogs get heartworm disease, and what do we as dog owners need to know about this parasite?

How do dogs get heartworm disease?

The parasitic worm that causes the disease is called Dirofilaria immitis. Dogs are it’s definitive host. The worm matures inside canines into adults. They mate and produce offsprings that continue living inside the dog. Mosquitoes are only intermediate hosts, and the worm lives inside them only for a short period of time in which they become infectious.

Adult worms live in the heart, lungs, and associated blood vessels of an infected animal.

Heartworm disease has been reported in dogs in all 50 states. But they are particularly common along the Atlantic and Gulf coasts from the Gulf of Mexico to New Jersey and along the Mississippi River.

The lifecycle of heartworms

After the infection, adult female worms release their offsprings into the dog’s bloodstream. Mosquitoes get infected after biting an infected dog. Over the next two weeks, the worm’s offsprings will become infective larvae while they are living inside the mosquito. Mosquitoes spread the disease by biting healthy dogs. It takes about 6 months inside the dog for the larvae to mature into adult worms. Adult worms mate, and release new offsprings, therefore completing their lifecycle.

Heartworm disease spreads only by mosquitoes. Therefore, dogs can’t get infected while hanging around another sick dog.

Heartworms can live inside dogs for 5 to 7 years. Adult heartworms look like strands of noodles or spaghetti. Males reach about 4 to 6 inches in length, while females reach about 10 to 12 inches.

In average, about 15 worms live inside an infected dog. However, in some cases the number can be much higher. Sometimes even reaching up to 250 worms.

The lifecycle of heartworms in dogs
The complete lifecycle of heartworms in dogs.

How to test dogs for heartworm disease?

The most reliable way to diagnose heartworms is with blood tests. Antigen tests detect specific heartworm antigens. Female worms release these antigens. The earliest you can detect them is five months after the infection.

READ MORE: Can A Dog Get Coronavirus?

Another way is by detecting microfilariae in the dog’s bloodstream. The earliest that you can detect heartworm disease using this method is about 6 months after the infection. Clearly because that’s how long it takes for the heartworms to develop from infective larvae into adults that produce microfilariae.

We certainly recommend annual testing. Ask your vet about your dog’s annual test. Surely they’ll be glad to help.

What are the symptoms of heartworm disease?

Depending on the number of worms, the symptoms can be mild or severe.

There are four classes (stages) of heartworm disease. The higher the class the more serious their condition is.

  • Class 1: No symptoms or mild symptoms such as an occasional cough.
  • Class 2: Mild to moderate symptoms. An occasional cough or tiredness after moderate activity.
  • Class 3: More severe symptoms. Your dog appears sickly. Persistent coughing, tiredness even after mild activity. Signs of heart failure are also common.
  • Class 4: Also called caval syndrome. A large mass of worms is blocking blood from following back to the heart. This condition is life-threatening and often deadly. The only treatment option is surgical removal of the worms.

If left untreated, heartworm disease damages the dog’s heart, lungs, liver, and kidneys. Eventually, ending lethal for the dog.

A representation of the bloodflow being blocked in dogs with heartworms, clearly showing it’s important to know how do dogs get heartworm
Blood flowing back to the heart is physically blocked by a large mass of worms.

What is the treatment for heartworm disease in dogs

FDA approved Melarsomine dihydrochloride. It’s available under the trade names Immiticide and Diroban. It treats dogs with class 1, 2, and 3 heartworm disease. Clearly not class 4.

In addition to this, Advantage Multi for Dogs is a topical solution applied to the dog’s skin. It’s FDA approved as well and helps dog get rid of microfilariae.

The treatment is quite expensive and can even cause some serious side effects such as blood clots. These side effects can potentially be life threatening. Despite this, no treatment is deadly. The side effects are rare and most dogs in class 1 and 2 recover.

But just like with any other disease, prevention is the best treatment!

There are different products available, and all require a vet’s prescription. Therefore, talk to your dog’s veterinarian and discuss the best possible prevention for your pup.