What are the signs of heartworms in dogs? This article will certainly answer that question in detail; But first let us say up front that if you have a beloved canine companion that you are responsible for, it is not wise to wait until the signs of this debilitating disease manifest in your pet.
Heartworm disease is preventable and prevention is greatly preferable to treating this dangerous mosquito-borne canine condition; Also the internal organ damage caused by these heart-dwelling parasites can be permanent.
What Is Canine Heartworm Disease?
Canine heartworm disease is a serious and potentially deadly ailment of dogs that is spread by mosquitoes. Not every mosquito is a carrier of the disease, but the mosquito is the intermediate host of Dirofilaria immitis which is the scientific name for the dog heartworm. 
Dogs are the most typical host mammal for heartworm disease. Heartworms that live inside an infected dog grow into adults (both male and female worms), which mate and produce offspring, all within the dog’s body. This puts the dog’s vital organs at serious risk.
Adult heartworms are long, spaghetti-like worms that live in an infected dog’s heart and pulmonary blood vessels. These internal parasites will eventually move into the lungs if left untreated. The adult female heartworms can grow to up to 14 inches (36 cm.) in length. The mature adult male heartworm is about half the size of the female.
Heartworms are of one the most dangerous parasites found in domestic dogs but they don’t just affect our precious pets. Wild canids such as wolves, coyotes, foxes, and jackals are also potential targets for this disease since it spreads from host to host by way of the ubiquitous mosquito.
You may be wondering how one little mosquito bite can result in a dog having worms of considerable length living in such a vital organ as the heart. It’s actually a cycle which takes several months to complete.
How are Heartworms Transmitted from Dog to Dog by a Mosquito?
The whole scenario begins with a dog already infected with heartworms and a hungry mosquito. We’ll call this dog “Buddy.”
- Buddy has adult heartworms in his heart. These heartworms mate and reproduce millions of microscopic offspring. These offspring, (or ‘baby heartworms’) are called microfilariae and they circulate freely in Buddy’s bloodstream.
- The hungry mosquito lands on Buddy for a blood meal and sucks up and ingests blood containing the microfilariae.
- Inside the mosquito, the microfilariae develop into an infective larval stage. This is why the mosquito is called the intermediate host of the heartworm.
- A couple of weeks later, this same mosquito lands on a different dog for a slurpy supper of canine blood. We’ll call this dog “Sophie.” She is healthy and heartworm free, but since she is not on heartworm prevention, she won’t be for long. When the mosquito begins feeding, the infective larvae enter Sophie’s body through the mosquito bite wound.
- Once inside Sophie’s body, the larvae begin to slowly migrate to the right side of her heart. Here they make themselves at home and are able to grow and develop into sexually mature adult heartworms.
- Within approximately 6 months time, Sophie’s heart is home to mature adult heartworms. These worms begin to mate and produce millions of microfilariae which circulate throughout her bloodstream. Soon another mosquito will land on Sophie for a meal.
- The cycle continues.
What are the Signs of Heartworms in Dogs?
A dog that has recently been infected with heartworm microfilariae by a carrier mosquito will typically not show signs of the illness right away. As the disease progresses however, the dog will begin to exhibit symptoms. It can sometimes take years for clinical signs to develop but it takes at least 6 months for the heartworms to mature and grow to a substantial size. Any time after that the worms begin clogging the right chamber of the dog’s heart, feeding off his blood, and affecting the pulmonary arteries and the dog’s lung capacity.
Signs of heartworms in dogs include:
- Uncharacteristic fatigue, even after moderate exercise
- A dry cough
- Decreased stamina
- Shortness of breath
- Lethargy
- Loss of appetite
- Loss of weight
These would be some warning signs that a pet parent might observe and most of them would be more noticeable following exercise. A veterinarian would likely hear abnormal heart and lung sounds when listening to the dog’s chest with a stethoscope.
The vet would need to draw a small amount of blood from the dog to test for heartworms. If the test(s) were to come up positive for heartworm disease, there is a treatment for it. Most infected dogs can be successfully cured but the treatment is expensive and intricate, and not without some risk. As mentioned earlier, heartworm prevention started early in the dog’s life (puppy hood) is by far the best option.
Heartworm Prevention for Dogs
All FDA approved heartworm prevention medications require an O.K. and a prescription from your veterinarian. Most veterinary clinics carry a variety of heartworm preventatives but you may be able to get them cheaper online.
There are 3 common kinds of heartworm preventative medications for dogs.
1.) The first is a monthly spot-on topical medication that the pet owner applies to the animal between the shoulder blades on the skin, rather than the fur. These medications are toxic if swallowed so the idea is to put the treatment on a place that the dog cannot reach to lick. The dog should also be isolated and kept away from other pets and children for a time after application and not allowed to try to rub the medicine off on furniture, or roll around in the grass immediately after.
Many of these topical monthly heartworm preventatives also have an active ingredient to eliminate fleas and ticks, as well certain intestinal parasites.
2.) There are also oral monthly heartworm prevention medications. These are available in tablet form or chewables. If you have a finicky eater you may be better off with the tablets that are small enough to hide in a bit of cheese or peanut butter. If you have a chow hound for a pet, he’ll most likely look forward to wolfing down his monthly “treat” with no trouble at all.
Many of these oral medications also serve more than one function. Some will not only eliminate the heartworm larvae but certain intestinal parasites as well and they contain an active ingredient for flea control.
3.) Injectable heartworm preventative is effective for up to six months with one injection. A licensed veterinarian must administer the dose to your dog. He or she should explain to you any warnings, possible adverse reactions, or side effects of the drug.
In any case, the good doctor should be able to advise you as to what heartworm prevention would be best for you and your dog. Whichever medication you choose, be sure to follow all label directions and let the vet know if your pet shows any aftereffects or sign of illness. To protect your dog even further from this unwanted disease, it’s always recommended having your dog tested for heartworms annually.
And if you are considering purchasing or adopting a puppy, be sure to get him or her started on heartworm prevention at an early age to prevent future heartache and heartbreak!
Thanks for visiting and learning about canine heartworm disease. Please leave any questions or comments or relevant experiences you may have in the comment section below. Thank you for visiting My Geriatric Dog!
