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Questions and Answers about Heartworm Disease in Dogs and Cats

What causes heartworm disease?

Heartworm disease is caused by a worm called "Dirofilaria immitis." Heartworms are most commonly found in dogs. However, they can infect a wide variety of mammals including cats, ferrets, sea lions, bears, foxes, wolves, coyotes, and even people. Adult heartworms generally live in the heart and major arteries of the lungs, although they may be found in other areas of the body.

How are heartworms transmitted?

Heartworms can only be transmitted from one animal to another by mosquitoes. Adult worms produce microfilariae (small, immature heartworms). Microfilariae generally are found in the blood of dogs and rarely in cats. The mosquito ingests heartworm microfilariae when biting an infected host (usually a dog). The microfilariae develop in the mosquito into "infective larvae" and are deposited with saliva on the skin as the mosquito is feeding. The infective larvae pass through the skin and migrate through the body tissues.

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Are all pets at risk?

Dogs are considered the preferred host of the heartworm. While the highest prevalence of heartworm infection is in areas with heavy mosquito populations, heartworm-infected animals can be found in all environments making heartworm disease a health consideration regardless of where you live. Ask your veterinarian for recommendations regarding testing and preventing this disease in your pet.

What are the signs of heartworm disease?

Many pets infected with heartworms may not show any evidence of infection in the early stages of the disease. Signs may appear eventually and may worsen over time. Early detection is important in managing your pet’s health.

Initially, dogs tend to develop a cough and experience difficulty breathing. They may exhibit decreased tolerance to exercise, develop fainting episodes or suffer severe weight loss. Since the heart and lungs are affected, many of the clinical signs seen are typical of heart failure, pneumonia or other debilitating disease. The severity and onset of clinical signs relate to three things: the number of heartworms present, the duration of the infection and the dog's response.

Clinical signs of heartworm disease in cats vary. Some cats do not show any significant clinical signs. Vomiting and/or respiratory signs (such as coughing and difficulty breathing) are seen commonly in chronic heartworm disease. Cats may have severe, acute disease with signs of respiratory collapse. They may suddenly die.

If your pet is heartworm positive and develops clinical signs, see your veterinarian immediately.

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How do I know if my pet has heartworms?

Routine testing for heartworm infection is done in areas where mosquitoes live and the prevalence of heartworm infection is high. An in-clinic blood test has been developed to aid in the diagnosis of heartworm infection. Ask your veterinarian about the Solo Step^® CH and Solo Step^® FH Heartworm Tests from Heska. Additional testing may be necessary.

My pet rarely goes outside. Can it be infected?

Indoor pets may have lower risk of becoming infected than outdoor pets due to reduced exposure to mosquitoes. However, heartworm infections have been reported in pets that rarely go outside. If a mosquito carrying heartworm infective larvae enters the house, it can bite your pet and the larvae may infect him or her.

When do veterinarians recommend testing for heartworm infection?

For your dog, veterinarians recommend testing for heartworm infection before beginning heartworm preventive medication, at regular intervals after the dog is on a preventive medication and when dogs have clinical signs suggestive of heartworm disease. In heartworm endemic areas, testing may be recommended as part of the annual physical examination.

For your cat, your veterinarian may recommend testing in any of the following situations:

• Prior to prescribing heartworm prevention medication
• Pre-anesthetic or pre-surgical screening
• When your cat has signs suggestive of heartworm disease
• When monitoring a cat with heartworm disease
• During an annual health check

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Can heartworm disease be prevented?

Fortunately, heartworm disease can be prevented, if preventive medications are started early and are consistently given throughout the pet's life. However, these medications will not eliminate existing infection. Knowing the heartworm infection status of your pet is an important part of keeping your pet healthy and fit.

What can be done if my pet has heartworms?

Medications to eliminate adult heartworms and immature heartworms are available. Once successfully treated, preventive medications and regular monitoring with the HESKA^® Solo Step^® Heartworm Tests should become part of your pet’s health maintenance plan.

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