Heartworm FAQs

June 17, 2015

Heartworms are among the most dangerous parasitic worms that can infect dogs. Hundreds of thousands of cases of canine heartworm disease are reported in the US every year. The disease is passed from infected dogs to other dogs by mosquitoes. That means all dogs are at risk for heartworm disease.

What is heartworm disease?

Heartworm disease in dogs (dirofilariasis) is a serious and potentially fatal disease. Heartworms spend their adult lives in the right side of the heart and the large blood vessels that connect the heart to the lungs. The adult worms block the heart and major blood vessels leading from the heart to the lungs, liver, and kidneys.

How do dogs get heartworms?

The disease is spread when a mosquito, previously infected by biting an infected (“reservoir”) dog, bites a dog and deposits tiny immature heartworms, called microfilariae, near the bite wound. They enter the wound, become larvae and migrate beneath the skin, eventually reaching the heart and lungs. These unwelcome intruders can eventuallygrow up to 12 inches in length.

Where are dogs at risk for heartworm infection?

All dogs are at risk for heartworm disease, no matter where they live – heartworms don’t discriminate based on geography. In the past, heartworm disease in the United States was primarily limited to the south and southeast regions. However, it is now found in all 50 states, in Canada, and worldwide, and is spreading to new areas each year¹. The American Heartworm Society notes that uncared-for dogs and certain wildlife can be carriers of heartworms. Mosquitoes blown great distances by the wind and the transportation of infected pets to different geographic locations can all contribute to the spread of heartworm disease².

What are the signs of heartworm infection?

Signs of heartworm disease can be subtle and difficult to detect until its later stages. An infected dog may cough or wheeze occasionally, and may seem unusually tired and unwilling to play, but these early signs of heartworm disease can easily be missed, and may be mistaken for something else. The only way to tell if your dog has been infected is to have a veterinarian administer a heartworm test.

As the disease progresses, signs begin to appear. Contact your veterinarian immediately if you notice coughing, difficulty breathing, sluggishness and less energy for exercise in your dog. Adult heartworms cause serious harm to your dog’s heart, lungs and certain internal organs. Left untreated, heartworm disease can result in loss of consciousness and death.

How are dogs tested for heartworm infection?

The most common method for heartworm testing is for a veterinarian to collect a small blood sample from a dog and evaluate the sample using a specialized test kit that identifies the heartworm antigen. Or, your veterinarian may use other types of tests that detect the presence of microscopic microfilariae, an early stage in the heartworm life cycle.

How can heartworm disease in dogs be prevented?

There are a number of heartworm preventive products on the market. Talk with your veterinarian to decide on the product that best suits your dog.

Can heartworm disease be treated?

Although it is possible to treat heartworm disease if a dog becomes infected, it is difficult, expensive and risky, particularly in dogs that have begun to exhibit clinical signs of infection.

What if my dog becomes infected with heartworms?

There are treatment options available to eliminate adult heartworms in dogs that have become infected. Treating dogs with heartworm disease starts with a thorough physical examination by the veterinarian. The veterinarian will then discuss treatment options with you. Typically, the dog is hospitalized during the treatment period. Because there is a risk of blood clots or worm debris blocking blood vessels from adult heartworm treatment, the dog must then remain quiet in close confinement for another four to six weeks after treatment. A second round of treatment may be required for some dogs. The veterinarian may also give your dog a treatment to rid it of the immature larvae that are circulating through the blood stream.