What is heartworm disease and how can it affect my dog?

Heartworm disease is exactly what the title says, worms in your dog's heart. Those worms are spread by mosquitoes. Mosquitoes are part of the life cycle of the heartworms, so where there are large numbers of mosquitoes, there are large numbers of heartworms. Those worms live in the right side of the heart. They keep that heart valve from closing completely and basically put your heart into heart failure, so your dog can be experiencing symptoms of heart failure because of heartworms.

Dr. Robert Gribble
Vets of East Texas

How would my dog catch heartworms?

Mosquitoes are the vector, which means they spread it, so they bite a dog that has heartworms, and those larvae will go through a life cycle in the mosquito, and then that mosquito can either put that back into the same dog or a different dog, and then that larvae will turn into an adult.

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

Signs in your dog can sometimes be nothing. Sometimes heartworms are referred to as the silent killer because you don't even know they're there. The average heartworm infection is about 40 worms, so you can imagine 40 worms that are about 12 to 15 centimeters long living in a heart don't do too well with longevity. Some of the signs are no signs at all, and the worst case symptoms are symptoms of heart failure, such as an abdomen getting bigger, full of fluid, coughing, and exercise intolerance.

What can be done to stabilize my dog's heartworm disease?

Prevention is the way to do it. We recommend, here in East Texas, year-round heartworm prevention. The preventions we use are very effective, and we recommend starting them at six or eight weeks old. If your dog already has heartworms, that's a different situation, as you need to get rid of the worms that are already there, as opposed to preventing them from showing up in your dog's heart in the first place.

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

We start that as puppies. When we do puppy vaccines, we give heartworm prevention. We boost those vaccines about a month later and give another heartworm prevention. When they get old enough to get their last puppy shots at around 16 weeks old, we give a heartworm prevention injection that lasts for six months. When that runs out, we move up to an injection that prevents heartworms for a full year.

How will a veterinarian diagnose my dog as heartworm positive?

There are a couple of tests. One is an antigen test, and the other is a microfilaria test. The antigen test tells us there are adult female worms in your dog right now. The microfilaria test is a blood sample that you look at under a microscope, and you can see small baby heartworms swimming in the blood. You can also perform an ultrasound of the heart if you suspect heartworms and get a negative test. There may be one or two worms that may not trigger a positive test, but you can see those worms with an ultrasound of the heart.

How often should my dog be tested?

We test every year at the vet on West Main, the vet on 4th, and the vet on Broadway. We run a blood panel on all of our patients every year, which checks the kidneys, liver, blood glucose, and gives us an idea of what's going on inside the heart. This also includes a test for heartworms and several tick-borne diseases. So yearly testing is what we recommend with all of our patients.

If my dog tests positive, do I need additional tests?

If your dog tests positive on an antigen test, we can also run a microfilaria test to see if there are babies because there are two different treatments: one to kill the babies and another to kill the adults. So we will need to test for adults and separately for circulating microfilaria.

If my dog is on heartworm prevention, do they still need yearly heartworm tests?

Technically, no. They don't need a heartworm test, especially if you're using the injection that lasts for an entire year because there are no lapses in coverage with that injection. However, it is a part of our blood panel, so we will get a test result every year. But as far as keeping them on heartworm prevention, it's not necessary to test every year, but it's part of our panel.

Is heartworms painful?

I'm going to say no. However, the symptoms it causes, such as fluid buildup in the abdomen and chest and symptoms of heart failure, are uncomfortable. Not being able to breathe well is not a comfortable situation. Is it painful? Pain is in the eye of the beholder.

Are there risks associated with the treatment of heartworm treatment or prevention?

Absolutely. When we kill those worms that have been living in the right side of your dog's heart, they immediately go as dead worms into the lungs. This can cause pulmonary embolism, which is bleeding in the lungs. Especially if there's an average infection of 40 worms, if 20 of those worms go at the same time into the lungs, that's going to be a problem. There is a very strict no-exercise part of treatment right after we kill those worms. It's very important to restrict activity because if your dog goes out and chases a ball and their heart starts racing, it is more likely to push a group of worms into the lungs, which is a serious problem that could lead to death.

What are the side effects to the medication used to prevent heartworms?

If there was one side effect that would probably be most common, although very uncommon, it would be an allergic reaction to the injection itself. Swollen lips, swollen eyes, similar to a vaccine reaction. It's treated like a vaccine reaction and gets better like a vaccine reaction. It does not last the entire duration of that shot.

How effective is heartworm prevention?

Heartworm prevention given on time every year is 100% effective unless you deal with a resistant worm, which is a possibility. The closer you get to the Mississippi River over in Louisiana, Mississippi, there are resistant worms emerging to older heartworm preventions that have been around for 20 or 30 years. They just lose effectiveness. The newer ones like moxidectin, which is what we use, and the injection that lasts for a year, has been proven effective even against resistant worm strains.

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

If you miss a dose of prevention, start them right back on it as soon as you realize. Missing a dose could lead to a window of infection that won't show up for about six months. So if you come in and we run our yearly testing and we get a positive, then we're going to say, okay, sometime between six and 12 months ago, there was a dose missed or we're dealing with a resistant worm.

What are the different stages of heartworm diseases?

Different stages have to do with the life cycle. Without getting too much into the biology of the life cycle, you have immature worms, which are created by adult worms in the body. They are called microfilaria. Microfilaria get extracted by a mosquito, go through another part of their life cycle in the mosquito, then that infected larvae is back into the dog and that larvae can turn into an adult. So basically, you have adults, microfilaria, and infected larvae.

Can my dog die from heartworm disease?

Absolutely. We see dogs dying every month from heartworm disease. In Northeast Texas, this is considered an endemic area. It doesn't get any worse than here. Maybe down on the Gulf Coast, it gets even more severe. If you don't prevent heartworms in this area, your dog will get heartworms.

Can my indoor dog get heartworms?

I don't know of that many dogs that stay indoors 100% of the time. Although you may consider your dog an indoor-only dog, they likely go outside to do their business. Some dogs stay with their own puppy pads, but that is a very small number of dogs. Mosquitoes can get inside your house, so heartworms can get inside your house.

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