How would my dog catch heartworms?

Mosquitoes transmit heartworm disease. A mosquito bites the dog, and if they have been infected with heartworms, they then inject the dog with the heartworm larvae, and over five to six months, it develops into the heartworms that live in the dog heart.

Dr. Shawn McCorkle
Summer Creek Animal Clinic

Can dog heartworms be prevented?

Yes, absolutely. Living in Texas, there's almost nothing we can do about getting rid of the mosquitoes, at least effectively enough to eliminate heartworm disease. Hence, our way of preventing heartworm disease in dogs is by putting them on heartworm prevention. These preventives kill the baby heartworms before they can develop into adults. You must keep up with dog heartworm prevention year-round in Texas because of our climate.

What are the signs in my dog that would indicate they may have heartworms?

Once your dog has adult worms that live inside the heart, which you can see in this picture, these little white spaghetti-looking things are the adult worms that live in the right side of the heart. And once the adults are in the heart, they can do a lot of damage over time. And one of the most common things we see is coughing. Dogs can be lethargic and have exercise intolerance, so they cannot go as long as they normally would. The main thing we're going to see once they're symptomatic is coughing.

How soon should I bring my dog in to see a veterinarian for heartworm prevention?

Heartworm prevention should ideally start by eight weeks of age, so if your dog's over eight weeks or eight weeks old, then we need to see them and get them started on heartworm prevention as quickly as possible.

How will a veterinarian diagnose if my dog has heartworms?

That's important. The only way that we can easily detect heartworms is by doing a blood test. The female heartworm releases an antigen that we can pick up on in the dog's blood. The vast majority of infections are going to be circulating heartworm antigens in the blood. A small blood sample allows us to detect adult worms, and then we know that the dog is infected.

It's vital to understand the life cycle of a heartworm. When the mosquito bites the dog, it takes five to six months for that worm to develop into the adult worm, and the adult heartworm is what we're able to detect in the blood. If your dog were infected within the last six months, the heartworm test today would not be able to pick up that heartworm.

If they've been off prevention and are an adult dog, we test them now and then again in six months to ensure that they're negative. I've personally owned two dogs that have been positive six months after I adopted them because of that window.

Why is early detection and diagnosis of heartworms so important?

Early diagnosis and detection are essential because early detection of adult heartworms often can allow us to intervene and treat the heartworms before they do significant damage to the heart and lungs. And if we can do that, we can usually have long-term success with minimal to no long-term complications.

If you still have other questions and you'd like to reach out to us, you can call us directly at (817) 523-1139, you can email us, or you can reach out on Facebook. But please do reach out, and we'll get back to you as fast as we can.

Heartworm Disease - FAQs

Dr. Shawn McCorkle
Summer Creek Animal Clinic

What are the different types of heartworm prevention for dogs?

The big categories to think of are the monthly oral preventions, such as a chew or tablet that you give monthly. There are a couple of topical options that you put on with a little liquid directly on the skin that get absorbed systemically to act as heartworm prevention. Then, there is one injectable heartworm prevention that's given under the skin that lasts for six or 12 months, depending on which product it is.

When should I start heartworm prevention for my dog?

Every dog, especially in Texas, should start heartworm prevention by eight weeks of age. If your pet's over eight weeks of age, then get them on prevention as soon as possible. Mosquitoes, which transmit heartworm disease, will bite a young puppy and an adult dog, so we need to start them by eight weeks.

How effective is heartworm prevention?

Most, if not all, FDA-approved heartworm preventions are incredibly effective—in fact, over 99% effective. That's very fortunate because, again, in Texas, heartworm disease is such a big deal. Having prevention that we can be very confident in is a very good thing.

Does my dog still need a heartworm test if they're on prevention?

That's always the question because heartworm preventions are so effective. The answer to that is yes because, especially in Texas, we have one of the highest incidences of heartworm disease in the entire country. And heartworm prevention is not 100% effective, so even if you give it consistently, I have had dogs come back positive. And this is true even when we were sure that the owners were giving it consistently. So that happens rarely, but it can. And realistically, many dogs, if not most dogs, are not on the prevention 100% accurately and on time all the time. These little lapses can turn into an issue as well.

Can prevention be used to clear a heartworm infection?

Yeah, that's a great question. If you get on the internet, you're going to see many talks about heartworm preventions being a slow kill heartworm treatment. Unfortunately, that is not the case. There has been some recent research with one topical product, as the ingredient moxidectin was shown to at least shorten the adult heartworm lifespan. But it's still not considered an adulticide or something that kills or treats the heartworms. Heartworm prevention is part of the treatment in the sense of preventing further infection, but it's not a treatment for adult heartworms. That is a different treatment that needs to be done that has a much higher likelihood of clearing the infection of the adult worms.

Are there any holistic or over-the-counter dog heartworm preventions?

At this point, no. There is not anything effective for treating heartworm disease. And so the simple answer to that is no, there's not.

Can I do anything in my dog's environment to reduce the risk of heartworm?

That's a great question because there is a vector for heartworm disease. If we could get rid of mosquitoes, that would get rid of heartworm disease. As you're likely aware, mosquitoes transmit all kinds of diseases. And if we could eradicate mosquitoes, there would be lots of diseases that we would be able to get rid of. Unfortunately, that's just not the case. So even a strictly indoor dog, which is rare, that never steps foot outside is still going to be at risk in Texas because mosquitoes fly. They can get into the house, bite your dog, and transmit heartworm disease. You can do things in the environment to reduce your mosquito exposure, which I think is helpful and useful. Still, it in no way makes it okay for your dog to not be on heartworm prevention because you can never guarantee there won't be a mosquito in the environment.

What should I do if I miss a dose of my dog's heartworm prevention?

If your dog's been on consistent heartworm prevention and you miss a single dose, the risks are going to be pretty low. We just need to get started back on heartworm prevention as quickly as possible. The best thing to do in that situation, because it does kind of depend on the specific circumstances, would be to contact your veterinarian and get their advice as to whether there should be an additional heartworm test. At least find out when the next heartworm test should be, depending on how long there was a lapse. But if you miss a few days here and there, it's not likely to be a big deal, but it is still crucial to try to stay on time as much as possible.

If you still have other questions and you'd like to reach out to us, you can call us directly at (817) 523-1139, you can email us, or you can reach out on Facebook. But please do reach out, and we'll get back to you as fast as we can.