As spring begins and temperatures begin to rise, it is important that we discuss heartworm disease. But what exactly is heartworm disease, and why does your dog need medication to prevent it? What is the big deal, anyways? This article will help clarify what heartworm disease is and why we recommend yearly heartworm prevention.

Heartworms are a parasite that is spread by mosquitos. The lifecycle begins when a mosquito feeds on a dog, in turn depositing heartworm larvae through the wound. The larvae circulate through tissues, eventually making its way to the heart and lungs, all the while maturing to immature adults. Once in the heart, the worms develop into sexually mature adults and begin reproducing, creating microfilariae that are released into the bloodstream. This time period can take up to 6-7 months. A mosquito will feed on the host again and ingest those microfilariae, which will mature inside the mosquito becoming larvae that are ready to infect a new host.

If a dog becomes infected, the adult heartworms can lead to both heart and lung disease due to the worms damaging the epithelium and plugging up major vessels or airways. Clinical signs can include coughing, difficulty breathing, exercise intolerance, collapse, and even death. Luckily, it is a disease that can be treated. However, there are a few hitches with heartworm treatment. First, it can sometimes be difficult to diagnose heartworm disease if there are no clinical signs. Our in-house tests can only diagnose heartworm disease if there are adult female worms present, and as mentioned before, this can take up to 6-7 months after initial infection. Thus, there is a window of time where a dog could be infected and not show up positive on the test. Also, treatment can actually be dangerous. When you are trying to treat heartworm disease you are in effect killing off large quantities of worms. This can lead to complications, including death, and often dogs need to be kenneled for periods of time during treatment in order to reduce the risk. Lastly, treatment can be very expensive.

Obviously, it is much preferable to prevent this fatal and difficult to treat disease. However, in order to dispense preventatives, we must first make sure that they are negative with a heartworm test. There is a danger in administering preventatives to dogs that are unknowingly positive (i.e. there is no up to date negative heartworm test). For example, if a patient has a high concentration of microfilaria, they could have a severe adverse reaction that could potentially lead to death. This, combined with the fact that we would want to be able to treat heartworm positive dogs appropriately, are reasons why it’s so important to test for heartworms prior to dispensing prevention. If you are unsure if your dog is able to begin receiving heartworm preventative, just ask your veterinarian!

Here at Healthy Paws Veterinary Clinic, we do recommend year round preventatives. There are a few good reasons for this. Many people will argue that there is no point in giving heartworm prevention during the winter months when mosquitos aren’t around. However, there are definitely some winter months that are unseasonably warm and allow mosquitos to fly around. Another reason is that sticking to year round HWP doesn’t allow people to forget about restarting it in the spring, or to have it pushed back to after the weather has already been warm. On another note, HWP will continue to control against roundworms and hookworms. We see a very high incidence of intestinal parasites in our area, especially with dog parks, doggie day care, and plenty of outdoor activities such as hunting. Plus, roundworms are very hardy organisms that won’t die off even with a freeze. Both roundworms and hookworms are zoonotic diseases, meaning they can be passed from animals to humans. Children, especially, are at risk of picking up roundworms or hookworms from the pet or the environment. Plus, intestinal parasites can cause clinical signs in dogs as well, ranging from loose stool and a pot-belly to failure to gain weight and anemia from blood loss.

But what about cats? In short, yes, cats can get heartworm disease, but the disease tends to be a quite different. The lifecycle is pretty much the same. However, they tend to have lower worm burdens, have smaller worms present, have higher incidence of single-sex infections, and infrequently have microfilaria present which means cats tend to be a dead end host. Because of the possible male-only infections and infrequent microfilaria, diagnosis with in house tests can yield a higher frequency of false negatives.

For the most part, cats do not get heartworm disease has much as dogs just because they are not exposed as much. However, heartworm disease in cats can cause sudden death and is often much underdiagnosed. It is possible even for indoor cats to become infected (mosquitos can get inside!). For outdoor cats, it’s a good idea to recommend a product that is multi-functional, such as Revolution, which will not only protect against heartworms but also intestinal parasites, fleas and ear mites.

In conclusion, heartworm prevention is an important part of the wellness care for your pet. We are more than willing to discuss what is best for your pet at your next wellness visit!