Heartworm disease, also known as dirofilariasisis, is a serious infection that can be fatal in dogs and cats. It is a blood borne parasite that progresses to worms living in your dog's heart, lungs and blood vessels. It can also affect wildlife such as coyotes, wolves, foxes and cats, which can help serve as reservoirs for the disease in our animals. This means that wildlife in our area can be the cause for exposure to our dogs. Heartworm disease can be prevented!
How is heartworm disease transmitted?
Mosquitoes are required for transmission of disease from one animal to the next. The mosquito bites an infected animal and ingests blood that contains the immature stage of the heartworm called microfilaria. Microfilaria are essentially baby worms that live and float around in an animals blood stream. The micofilaria in the mosquito mature for 10 to 14 days before moving into the mosquito's mouthparts. The microfilaria infected mosquito then injects the parasite into the next host when it bites them for a blood meal.
What happens to a dog infected with heartworm?
Once a dog has been infected with microfilaria they circulate within the blood vessels. They can clogged vessels and can injury the liver and lungs. It takes about 6 months for the microfilaria to mature into adult worms.
The adult worms live in the heart and the large blood vessels that supply the blood to the lungs (called the pulmonary arteries). This makes the heart work harder to circulate blood to the lungs which can cause pulmonary hypertension and heart failure. The heartworms can also cause a physical barrier for the valves of the heart.
The heartworms and microfilaria also can cause an inflammatory reaction from foreign material being in the dog's body. This can cause damage primarily to the liver and kidneys.
What are clinical signs of heartworm disease?
Typically signs of heartworm disease do not become present for several years. As the number of heartworms increases and the damage to the heart and lungs becomes more significant signs will start to emerge.
mild persistent cough
exercise intolerance- unable to exercise as long or recover as fast
shortness of breath
weight loss
anorexia or lack of appetite
How is heartworm disease diagnosed?
All dogs should be tested for heartworm disease yearly starting at 7 months of age. If an adult dog is adopted it should be tested at the time of adoption and then 6 months later. Testing should be done yearly even if your dog is actively taking heartworm prevention. The test is performed on blood to determine the presence of heartworm antigen. The test specifically looks at the proteins on female adult worms. If this test is positive, additional tests such as testing for the microfilaria, chest x-rays, and full blood panels may be recommended.
Treatment for heartworm disease
The gold standard of treatment includes treatment with a medication called Melarsomine to kill the adult heartworms. This is done by 3 injections, one injection then waiting 30 days, then another injection followed by the last one 24 hours later. These injections are very painful (and expensive) and dogs are usually hospitalized for the days they are treated to monitor for any adverse effects or allergic reactions.
Dogs will also be treated with an antibiotic called Doxycycline to help Wolbachia, a bacteria that affects the adult heartworms.
There are other protocols that many veterinarians use that are called "slow kill" protocols. These protocols take a year or more to fully kill all the adult heartworms, which means that the potential for complications is prolonged and restrictions for your dog last longer.
While being treated for heartworm disease is extremely important to keep them as calm and quiet as possible to avoid the risk of complications from the adult worms being killed and circulated in the vessels.
For full detailed treatment recommendations visit The American Heartworm Society website.
HEARTWORM DISEASE IS PREVENTABLE!
All dogs over the age of 8 weeks old should be on continuous heartworm prevention. Several options are available in various forms such as oral, injectable or topical preparations. Oral and topical preventatives are given monthly and the injectable preventatives are given every 6 or 12 months depending on the age of your dog. Heartworm preventatives should not be stopped even when the weather is colder, unless directed by your veterinarian.
References: Heartworm in dogs https://www.heartwormsociety.org/heartworms-in-dogs#how-do-monthly-heartworm-preventives-work
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