Understanding Heartworm Disease: What Pet Owners Need to Know

by Jon Scaccia November 5, 2024

Heartworm disease is one of the most serious parasitic threats to dogs, causing severe health issues and even death. It’s caused by Dirofilaria immitis, a parasite transmitted through mosquito bites. These worms live in the heart, lungs, and blood vessels of affected animals, creating significant health problems. While heartworm disease is a growing concern, the good news is that prevention is simple, and treatment options have improved over the years.

What Exactly Are Heartworms?

Heartworms are foot-long worms that thrive in the hearts and lungs of infected animals, primarily dogs. Once inside the body, they grow and multiply, eventually causing lung disease, heart failure, and damage to other organs. A single dog can harbor hundreds of these worms, and the more worms present, the more severe the disease becomes.

Dogs are the primary hosts for heartworms, but cats and other animals like wolves, foxes, and even sea lions can also be affected. In rare cases, heartworms can even infect humans, though the risk is low.

How Heartworms Spread

Heartworm disease is transmitted through the bite of an infected mosquito. When a mosquito bites an infected animal, it ingests tiny baby worms known as microfilariae. These microfilariae grow inside the mosquito for about two weeks before becoming infectious larvae. When the mosquito bites another dog, these larvae enter the dog’s bloodstream, eventually growing into adult heartworms.

Infected dogs can spread the disease by hosting heartworms that continue the life cycle when mosquitoes bite them. This means that any dog, even one who never leaves your backyard, can be at risk as long as mosquitoes are present.

What Happens to Infected Dogs?

Once inside a dog, heartworms grow and settle into the heart and lungs, where they mature into adults. As they reproduce, they clog major blood vessels and damage lung tissue. Over time, this causes severe respiratory and cardiovascular issues. Symptoms of heartworm disease can range from mild coughing and fatigue to more severe signs like difficulty breathing, fainting, or sudden death.

In advanced cases, dogs may develop a condition called “caval syndrome,” where the heartworms block blood flow, causing life-threatening complications that require emergency surgery.

Prevention is Key

The good news? Heartworm disease is entirely preventable with regular use of preventive medication. Veterinarians recommend giving dogs heartworm prevention year-round, even in areas where mosquitoes are less active in colder months. Preventive medications work by killing the larvae before they grow into adult heartworms. These medications come in various forms, including monthly chewable tablets, topical solutions, and long-acting injections.

Preventing heartworms is not only easier than treating the disease but also much safer for your pet. Treatment for an existing heartworm infection can be costly and involves multiple rounds of injections that can be taxing on a dog’s body, especially if they’re already sick.

Treatment for Heartworm Disease

If your dog does become infected, it’s crucial to act quickly. The most common treatment involves a series of injections with a medication called melarsomine, which kills adult heartworms. This process can be dangerous because as the worms die, they can cause blockages in the blood vessels, leading to complications. For this reason, strict exercise restriction is necessary during treatment.

In some cases, dogs may need additional medications like antibiotics to kill a bacteria (Wolbachia) that lives inside heartworms, as well as anti-inflammatory drugs to manage the immune response to the dead worms. Dogs with severe heartworm infections may also require surgery to physically remove the worms from the heart.

Heartworm in Cats: A Subtle Threat

Although heartworm disease is more common in dogs, cats are also susceptible, though the disease manifests differently. Cats usually have fewer adult worms, but even a small number can cause serious health problems. Unlike dogs, cats can experience sudden respiratory failure due to heartworms, often without showing previous symptoms. Unfortunately, there is no approved treatment for heartworms in cats, making prevention even more critical.

The Importance of Regular Testing

Even if your dog is on preventive medication, annual heartworm testing is essential. No preventive is 100% effective, and testing ensures that if your dog does become infected, it’s caught early before the disease progresses.

Testing is quick and involves a simple blood test to check for the presence of heartworm antigens, which are released by adult female worms. The earlier heartworm disease is detected, the better the chances of successful treatment.

Join the Conversation

Have you had any experiences with heartworm prevention or treatment? How do you protect your pets from parasites like heartworms? We’d love to hear your thoughts and stories in the comments or on social media.