Heartworm Disease in Dogs Is Deadly But Preventable

Posted by Christy Caplan
dog and heartworm

Heartworm disease (Dirofilaria immitis) is a potentially fatal disease in pets in the United States according.

Heartworms have been found in all 50 states, although certain areas have a higher risk of heartworm infection than others. With that in mind, heartworm prevention is simple and will save your dog's life.

These foot-long heartworms cause severe lung disease and inflammation, heart failure, and damage to other organs in the body. They live in the lungs, heart, and associated blood vessels like the pulmonary arteries.

Mosquitoes carry the parasite that causes heartworm disease (from animal to animal). The life cycle of a heartworm begins when a mosquito bites an infected animal carrying heartworm microfilariae in its blood. If that mosquito bites another cat or dog, it transmits the larvae to that animal.  

As reported by the American Veterinary Medical Association:

"Heartworm is a preventable, but serious and potentially fatal, parasite that primarily infects dogs, cats and ferrets. It can also infect a variety of wild animals, including wild canids (e.g., foxes, wolves, coyotes), wild felids (e.g. tigers, lions, pumas), raccoons, opossums, and pinnipeds (e.g., sea lions and seals), as well as others. There have been documented human infections, but they are thought to be rare and do not usually result in signs of illness."

Heartworm and dogs

Common Symptoms

Owners may not catch symptoms right away as they are very subtle in the beginning. In the early stages of the disease, many infected dogs show few symptoms or no symptoms at all. The longer the infection persists, the more likely symptoms will develop. 

Clinical signs of infection in dogs include a chronic cough, lack of energy or endurance, difficulty breathing, loss of appetite or weight loss, or vomiting. These signs can point to many diseases so it's important a veterinarian perform diagnostics immediately. 

Heartworm disease is divided into 4 classes.

  • Class I: Symptoms are often asymptomatic, meaning they exhibit no visible symptoms, or may only exhibit minimal signs such as an occasional cough.
  • Class II: Patients typically include coughing and intolerance to a moderate level of exercise. (think asthma!)
  • Class III: May show a generalized loss of body condition, more extreme exercise intolerance, labored breathing, and a pot-bellied appearance associated with fluid accumulation in the abdomen as a result of right-sided heart failure.
  • Class IV: May have a condition known as caval syndrome in severe cases caused by the presence of so many worms that they block the flow of blood into the heart. Surgical removal is needed at this stage of the infection. (Why heartworm preventive care is so important).

Diagnosis Requires a Blood Test

 A simple blood test will diagnose heartworm disease but it's important to note that diagnostic tests (e.g. chest X-rays, urinalysis, complete blood count) are essential to determine if the dog can safely undergo heartworm disease treatment. Your veterinarian will determine which diagnostics (heartworm tests, antigen tests) are necessary. 

The Oregon Veterinary Medical Association (OVMA) explains:

"Your veterinarian may perform a blood test to determine whether your pet has the disease. A blood sample is tested for the antigens (proteins) produced by adult heartworms. The sample may also be examined under a microscope for the presence of the heartworm larvae."

Treatment for dogs with severe heartworm disease may require antibiotics, pain relief medications, special diets, diuretics to remove fluid accumulations in the lungs, and drugs to improve heart function prior to treatment for the heartworms. No one wants their dog to suffer from this horrible and preventable disease. 

The OVMA also reports:

"The goal of treatment is to kill both the adult heartworms and the larvae. American Heartworm Society guidelines recommend "doxycycline and a macrocyclic lactone prior to the three-dose regimen of melarsomine...for treatment of heartworm disease in both symptomatic and asymptomatic dogs."

Heartworm Disease is Preventable 

Year-round heartworm prevention is the solution. And heartworm preventative medication can be recommended by your veterinarian. 

The American Heartworm Society recommends year-round heartworm prophylaxis for maximal effectiveness. If seasonal treatment is chosen, the administration should begin at least one month prior to the anticipated start of heartworm transmission and depend on the product used.

Pet owners can find more information about heartworm and heartworm treatments on the American Heartworm Society's website

What heartworm preventative do you use? Please leave in the comments below!

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Heartworm Disease in Dogs Is Deadly But Preventable