Heartworm Disease and Prevention

preventing heartworm

Dr. Leslie administering a monthly heartworm medication.

We want you to have easy access to more information about heartworm disease and the advantages of prevention over treatment.

In this post we dispel misconceptions about heartworm, write about what you can do to prevent heartworm, and briefly describe the protocol if the disease occurs. Additionally we’ll give you some links to online resources if you would like to research this further.

As always, our primary message is that we are available to talk with you about any questions or concerns you have about your pet’s health and well-being.

Heartworm Disease and Prevention

Heartworm is a very serious disease in pets and can be life threatening. The prevalence of heartworm in the last decade has increased dramatically in the Chicago area, even though it is an extremely preventable disease. The American Heartworm Society provides maps of the incidence of heartworm in the United States – as well as past years for comparison.

What is Heartworm?

A common misconception about heartworm is that it is transmitted by fleas, or by the ingestion of contaminated feces, or of a worm itself. It is actually transmitted by mosquitoes, and it only takes one bite by an infected mosquito.

The heartworm life cycles consist of an adult female worm living in a host such as a dog, wolf, coyote, or fox. The adult female produces microfilaria that travel through the host’s bloodstream. When a mosquito takes a blood meal from an infected animal, the microfilaria are ingested as well. In the mosquito, they mature into larvae over a period of 10 to 14 days – the mosquito is now considered infective. When the infected mosquito bites a susceptible animal, the larvae enter through the skin and bite wound of the new host.

It takes approximately 6 months for the larvae to mature into adult heartworms.

The larva migrate through tissue of the infected host until they become a juvenile worm. At this point they enter the host’s blood stream, making their way to the heart (and pulmonary arteries) – hence the name “heartworm.” Once they are in the heart/lungs, they mature into the adult worm. This is why we test our patients for heartworm annually. The most common heartworm screening test identifies the presence of adult heartworms.

How does Heartworm Affect my Pet?

Heartworm infection in the dog can cause damage to the heart, lungs, kidneys, eyes, central nervous system, and the systemic circulation. Affected animals may have no clinical signs initially. In the earlier phases of the disease they may develop a cough, exercise intolerance, or weight loss which may or may not be due to a loss of appetite. In more serious cases, they can go into heart failure, have severe lung disease or have a sudden cardiovascular collapse.

Heartworm disease in the cat can present with mild signs such as a cough, vomiting, decreased energy or weight loss.

Heartworm Testing

For dogs, heartworm disease can be detected by routine blood screening tests, recommended yearly.

It requires a small blood sample and results return within 24 hours.

The screening test detects adult heartworms, so if there is concern of exposure it is important to test a patient 6-7 months after the exposure occurred. It is also important to test patients prior to beginning a heartworm preventive medication program, unless they are under 6 months of age.

Annual testing is necessary to allow early treatment if heartworm disease is detected as well as to ensure the preventive medication given has been successful.

If a patient is positive for heartworm disease, dogs with microfilaria could possibly have a reaction to the preventive. Our treatment recommendations will account for this possibility.  The earlier heartworm disease is detected and treated, the better it will be for the patient.

Treatment of a heartworm positive patient

Heartworm disease is a successfully treatable disease in most dogs, but there may be secondary life threatening complications.   We determine a treatment plan by the classification of the heartworm disease in the given patient using clinical symptoms and diagnostic testing results. Once the stage is determined a treatment plan is individualized for each patient.

The treatment and medical monitoring does take several months before a final resolution is achieved. Since heartworm disease is preventable, prevention is always the desired form of management.

Unfortunately, there is no safe treatment for heartworm disease in cats.

The indoor/outdoor cat should be tested and placed on preventive medications.

Heartworm Prevention

Routine prevention eliminates circulating larva before it becomes an adult worm and reaches the heart – this can occur in as little as 51 days. This is why keeping a strict preventive regimen is extremely important. This typically requires a simple oral preventive (often a chewable “treat”) our patients can enjoy once every 30 days.

Many heartworm preventives also have other medications paired with them to control intestinal worms as well.

Each of our patients is assessed and their individual health conditions is taken into account prior to us recommending and instituting a specific heartworm prevention.

Please call us with any questions, or visit the American Heartworm Society for more information.