Heartworms are long slender worms that live in the heart and large blood vessels of the lungs. They can measure over 12 inches long! These dangerous parasites can affect mammals including dogs, cats, ferrets, coyotes, wolves, foxes, etc. and are very common throughout the United States. Heartworms are one of the most damaging parasites in dogs but they are almost 100 percent preventable.

Heartworms are common throughout the United States, especially in the Southern U.S. Every year, approximately 300,000 dogs are diagnosed with heartworms in the United States. In 2018 1 out of 40 dogs in Dallas County tested positive for Heartworms.

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Heartworms are spread by mosquitos. When an infected mosquito lands on your dog to take a blood meal, they will pass the microfilaria (immature, young worms) into your dog through the bite wound. The microfilaria will migrate around the body as they grow into adult worms. After several months, the adult worms will eventually end up in the right side of the heart, where the live permanently.

Mosquitos can get inside your home so both indoor and outdoor pets are at risk for heartworm infection.

Heartworms affect how blood flows through the body, especially in the heart and lungs. This can affect the heart and lungs but also other organs such as the kidneys and liver. Heartworm infection will result in permanent damage to your dog’s heart and lungs. These changes can lead to lung disease, heart failure, disease in other organs and, in some cases, result in death.

Signs of heartworm disease may not be present right away. Typically signs will worsen over weeks to months.

• None
• Dull, coarse hair coat
• Shortness of breath/tire easily especially with exercise
• Coughing (occasional to constant)
• Changes on lab work and x-rays

Once heartworm disease has been confirmed, either by the presence of microfilaria or after sending blood to a lab for a second heartworm test, your dog can begin the process of heartworm treatment. This process begins with a complete physical exam and may include additional lab tests and x-rays. This will help determine the physical status of your dog and their internal organs and can help your veterinarian make the best recommendation for treatment. Heartworm treatment combines several therapies to achieve death of the adult heartworms as well as the microfilaria.

Heartworm Prevention: Your dog will be started on a specific heartworm prevention immediately. This is a once-monthly medication given by mouth or on the skin, which will kill the microfilaria before they reach the heart. This medication will only prevent more adult worms, it will not kill the adult worms living in the heart and lungs. This medication will need to be given year round for the remained of your pet’s life in order to prevent future infection.

Doxycycline: This is an antibiotic that is commonly given in the beginning of heartworm treatment to help kill a bacteria known as Wolbachia. This bacteria is associated with heartworms and is thought to help with heartworm development, reproduction, and long term survival of the adult heartworms. When the adult heartworms die, Wolbachia is released and can result in severe inflammation. Treating with doxycycline prior to heartworm treatment will likely decrease the inflammation in the lungs following death of the adult worms.

Melarsomine: This preferred method for heartworm treatments involves three injections of a medication called melarsomine (Immiticide, Diroban). This is an arsenical chemotherapy agent that is given into the large muscles near the hips. This treatment will kill the adult worms quickly. This stops reproduction treatment of heartworms. This protocol is more than 98% effective in eliminating adult worms.

Your dog will need STRICT exercise restriction during the 12 weeks of treatment. This means leash walks only – no running, heavy playing, etc. Exercise restriction will decrease the chances of complications during the post-treatment period. Some of these complications can be life threatening.

It is important to know that the above treatment is recommended for the majority of patients diagnosed with heartworm disease. Without treatment, your pet will be started on heartworm prevention to kill the microfilaria only. They may also be started on other medications at the time of diagnosis depending on the veterinarian’s recommendations.

Only the microfilaria are killed with prevention. This means that the adult heartworms continue to live in the vessels of your pet’s heart and lungs until they die naturally. In dogs, adult heartworms can live for 6-7 years. The longer adult worms live inside your pet, the longer permanent changes will take place inside the heart and the higher the risk for serious disease and death.

If left untreated, heartworm disease will decrease the quality of life for your dog and may lead to death, we recommend scheduling an exam to start the treatment process.