Heartworm in Dogs: Why You Shouldn’t Wait Until There are Symptoms

Heartworm disease is a dreaded diagnosis that can mean extreme discomfort for your dog, but it’s also a disease that is highly preventable. Thanks to effective monthly preventatives, dogs are suffering from heartworm disease far less frequently and enjoying a higher quality of life than ever before.

However, no preventative measure is 100% effective, and the risk for heartworm disease, particularly in the Gulf South, is very high. Therefore, dog owners must know the signs and symptoms of heartworm so quick action can be taken when suspected.

Transmission of Dog Heartworm

It’s first important to understand how dogs contract heartworm. Infected mosquitos transmit 5 to 10 tiny worms into your dog’s skin when they bite. Those worms travel through your dog's body into the bloodstream and eventually become adult worms. The adult worms can be up to 12 inches long and settle in the pulmonary arteries on the right side of the heart, causing heart and lung distress.

Since mosquitoes are the primary transmission vectors of canine heartworm, owners should take precautions when taking their dog camping, hiking, or outside to play at dusk when mosquito activity is at its peak.

Signs of Dog Heartworm

Heartworm is a parasite that lives in the heart. Unfortunately, dogs rarely exhibit symptoms during the early stages of heartworm disease. By the time a dog owner notices the signs, it's likely advanced and the dog is very uncomfortable. Heartworm disease severely impacts a dog’s health, compromising the heart, lungs, and circulation; therefore, annual screening and monthly preventatives are essential.

Early signs of dog heartworm disease include:

• Difficulty breathing
• Persistent dry or moist cough
• Weight loss
• Nose and/or mouth bleeding

Middle to late-stage symptoms of dog heartworm disease include:

• Abnormal heart and lung sounds
• Enlarged liver or heart
• Panting at rest
• Exercise intolerance
• Fluid backup into the lungs and abdomen

A dog can go from mild to severe symptoms fairly quickly. As the heartworm disease progresses, a slight cough may develop, followed by more moderate to severe symptoms. 

The Importance of Early Detection

Early detection is vital since heartworm is fatal if unnoticed or ignored. As time passes and it remains untreated, the number of worms will continue to multiply. Early detection and diagnosis are essential to avoid more serious symptoms and severe complications that can lead to death. All dogs should be tested annually, but a dog should be examined immediately if heartworm disease is suspected. 

Treating Dog Heartworm

Treating heartworm disease can be complicated, with determining the stage being the first priority. A veterinarian will conduct ELISA tests, which test for adult female worms. Once a positive result is returned, a veterinarian will look at the blood for baby worms, called microfilaria, circulating in the body. Those baby worms are what a mosquito picks up when it bites your dog, eventually transferring them to another dog.

Those two positive indicators confirm heartworm disease, then treatment begins.

There are three phases to dog heartworm treatment:

• A veterinarian will administer medication to prevent further infestation.
• Doxycycline antibiotic begins to kill the bacteria the heartworm is living off. This is a critical step since worms need to be killed very slowly, as there are often many of them, and they're each approximately 12 inches long. They cannot be killed too quickly, or the dog may experience complications.
• Eventually, a veterinarian will administer three injections of an immiticide (generally in 2 stages spread over 2 months).

Heartworm treatment can take a few months since it requires multiple injections a certain number of months apart. It is also an investment of time and attention at home when the dog must avoid strenuous activity.

Heartworm Prevention

Dog heartworm is preventable with oral tablets or injectable medications that prevent the larvae from developing into adult heartworms. While no prevention is 100 percent effective, oral or injected preventatives exponentially decrease the likelihood of contracting heartworm.

Prevention begins as early as eight weeks old at a puppy’s first vaccine appointment and should continue throughout the dog's life. When mosquitoes bite a puppy or adult dog and deposit baby worms into their skin, they migrate over two months before getting into the bloodstream. While they're still in the skin, they're susceptible to being destroyed by heartworm preventatives, which is why they are started so early in the puppy stage. The dog may get infected, but the parasite is destroyed before it does any damage.

The American Heartworm Society is a trusted resource for heartworm insight and information.