New Hope for Treating Dogs with Heartworm

New Hope for Treating Dogs with Heartworm


Heartworm can be a devastating disease for dogs. Some dogs can be treated, but many dogs are often euthanized when they test heartworm-positive.

Many dogs who become infected with heartworms stand a strong chance of dying. However, the University of Illinois shelter medicine program has an affordable treatment option that could be effective for some dogs.

What is heartworm?

Heartworms are worms that live in the heart, lungs and the associated blood vessels of the animals they infect. This results in heart failure, lung disease and damage to other organs of the animal’s body. Worms can be found in many mammal species such as: Wolves, coyotes, foxes, sea lions, dogs, cats and ferrets.

They can also be found in humans but it is extremely rare. They are spread through mosquitoes, and transmission often occurs when mosquitoes bite a wild animal and pass the larvae on when they bite a domesticated animal.

Why shelter dogs with heartworm are euthanized

One of the reasons that shelter dogs typically are euthanized when tested positive for heartworm is due to the cost of the treatment procedure. It requires surgical removal by a boarded cardiologist. Although it’s a minimally invasive surgical procedure, it’s expensive.

Plus, the current standard for treatment of heartworm requires multiple drugs that take three separate sessions to complete. Overall, it takes at least three months to eliminate heartworms and a full six months before the dog can be retested.

New heartworm treatment protocol

A new protocol for the treatment of heartworms was published in the Journal of Parasites and Vectors by Molly Savadelis of the University of Georgia. This new protocol provides a new treatment option that is less expensive than previous methods and may provide a way to treat shelter animals rather than euthanize them.

The new protocol involves a combination of two drugs: Advantage Multi® for dogs (10% imidacloprid + 2.5% moxidectin) and doxycycline. The new protocol is referred to as “moxi-doxy.”

Dr. G. Robert Weedon is a veterinarian at the University of Illinois shelter medicine program who oversees its operation. Weedon and his team have adopted this approach at their shelter.

“When this protocol was completed in the study, all previously infected dogs tested negative for heartworm within ten months,” Dr. Weedon told the College of Veterinary Medicine at the University of Illinois.

“Moxi-doxy offers us another great tool with which to treat heartworm-positive dogs. With this protocol in a shelter setting, we can save resources and save lives,” Weedon said.

However, Dr. Ryan Fries, a boarded cardiologist at the Veterinary Teaching Hospital warns that this new alternative is not a silver bullet for all situations.

“It is great that we continue to look for ways to treat this devastating disease. Moxi-doxy is a great protocol for some dogs and owners; however, each case is unique and this protocol may not be appropriate for all dogs in all stages of heartworm disease,” Fries said.

Why heartworm treatment is problematic

Treating dogs for heartworm can be costly. According to the American Animal Hospital Association, the cost of treating a dog with heartworm can range from $400-1,000. And in some cases, can be even higher when you consider the cost of multiple veterinarian visits, as well as, blood work, x-rays, steroid injections, antibiotics and hospitalization. There can also be added expenses during the recovery period, which can be up to 6 months.

Secondly, treating heartworm can leave lasting effects on the dog’s heart. Not only that, but killing the heartworm releases bacteria into the dog’s body and sets off an inflammatory response which can affect its lungs and kidneys. This is why antibiotics and corticosteroids are necessary for treatment.

Third, heartworm treatment only kills off the adult worms. Ongoing and continuous preventative treatment is necessary to kill off smaller larvae. This preventative treatment for larvae is also necessary before initiating treatment on adult heartworms.

Current heartworm treatments

Once the preventative part of treatment for killing off heartworm larvae, as well as, corticosteroids and antibiotics to deal with your dog’s immune response, the next step is to treat the adult heartworm. Currently, there is only one drug that has been approved by the Food and Drug Administration (FDA) for killing adult heartworms and dogs.

This is also why the treatment by the University of Illinois is so promising – as it offers an additional alternative treatment. The current FDA-approved drug, melarsomine, is an organic arsenical compound. The drug is typically injected into the dogs lumbar-area muscles of the back.

Certain geographic regions are more prone to heartworm

In the United States, particularly in southeastern and Gulf Coast areas, as well as the Mississippi Valley, dogs are at higher risk for heartworm infection. Western areas of the United States are less prone to heartworm, but not completely immune.

How is heartworm spread?

Heartworm is generally spread by mosquitoes. When wild animals such as wolves, coyotes, foxes, and dogs or cats that already have heartworm disease are bitten by mosquitoes, the mosquitoes pick up microscopic baby worms called microfilaria that are released by the adult worms and are circulating in the bloodstream. Then, these mosquitoes bite a dog or a cat and then pass these larvae onto that animal.

After an animal was bitten, it takes approximately 6 months for the larvae to develop into adult heartworms. Mature heartworms can live for 5 to 7 years in dogs and up to 2 or 3 years in cats. The lifespan of the worms makes each mosquito season potentially more dangerous due to the increasing number of worms and the likelihood of an infestation getting passed on to your pet.

Signs of heartworm disease

In the early stages of heartworm disease, your dog will show few symptoms, if not no symptoms whatsoever. However, as the disease progresses, dogs who are heavily infected with heartworms will begin to show signs.

Some signs of heartworm disease are: Decreased appetite, weight loss, a mild persistent cough (soft, dry), easily becoming fatigued, lack of energy, inactivity or lethargy, rapid or difficult breathing, bulging at the chest. Your dog’s belly may swell due to excess fluid in the abdomen. As heartworms begin to block blood flow to the heart, your dog could have cardiac failure.

Another sign of impending cardiovascular collapse is called “caval syndrome” which manifests in a sudden onset of labored breathing, pale gums, and dark bloody or coffee-colored urine. Such a condition requires immediate surgical removal of the heartworm. Unfortunately, few dogs survive this level of infection.

Testing for heartworms

Your veterinarian will test your dog for heartworm through a simple blood test, which can be done during your dog’s annual or semi-annual checkup. If your dog tests positive, treatment can be initiated.

Stages of heartworm disease

Heartworm disease is graded in classes 1-4 with 4 as the most serious level.

Heartworm can be prevented

Heartworm infection is preventable through the use of monthly heartworm prevention medications and yearly testing. Not only that, but many of the preventative medications also include ingredients that also protect against intestinal parasites such as roundworms, whipworms and tapeworms.  The American Animal Hospital Association says the average cost of heartworm preventative medications runs between $5-$15 per month. This equates somewhere between $60-$180 per year.

Keep in mind that preventative heartworm medication must be ongoing for the life of your pet. If your dog stops taking the medication, it will be at risk of contracting heartworm. Secondly, even if your dog has had previous treatment for heartworm, it will always be susceptible to contracting them again unless you maintain a constant regimen of preventative medication.