How Do Dogs Get Heartworm? Causes And Treatment

How Do Dogs Get Heartworm? Causes And Treatment

Heartworm disease is a serious and potentially fatal infection that can affect dogs and other mammals. It is caused by a parasite called Dirofilaria immitis, which is transmitted through the bite of an infected mosquito. If left untreated, heartworm disease can lead to serious health problems and even death in dogs. In this article, we will discuss the causes of heartworm disease in dogs, how it’s treated, and what you can do to help protect your pet from this dangerous condition.

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Heartworm is a parasitic infection spread by mosquitoes. It can affect both dogs and cats and can be life-threatening. In dogs, heartworm is a roundworm (Dirofilaria immitis) larvae infection that usually settles in the heart, lungs, and associated blood vessels.

Dogs can get heartworm by coming into contact with an infected mosquito through outdoor activities such as walking, playing, and running. The mosquito bites the dog and then injects the larvae, which enter the bloodstream and settle in the major organs. At this point, your dog will not show signs of infection.

Treatment of heartworm is possible but must be done under veterinary supervision. Treatment typically consists of a series of injections that kills the adult worms. As well, your veterinarian may also suggest a preventative medication that will help to protect your dog from further infection.

It’s important to note that heartworm is preventable. Speak to your veterinarian about giving your dog heartworm preventatives, such as tablets or spot-on. These treatments should be given monthly, year-round.

What is Heartworm Disease?

Heartworm Disease is a serious and potentially fatal disease caused by an infestation of parasitic worms, also known as heartworms. These worms are often spread by mosquitoes and will migrate to the lungs and the heart of a dog, resulting in damage to the organs and decreased activity levels. Dogs should be tested regularly for Heartworm Disease, and if possible, should be vaccinated to prevent infection.

How Common Is Heartworm In Dogs?

Heartworm is unfortunately a fairly common problem in dogs, especially in areas with higher mosquito populations. It’s estimated that more than 1 million dogs in the United States are infected with heartworm each year. However, with the help of regular preventative treatments, it is possible to protect your dog and keep them safe from this deadly disease.

Can Dogs Get Heartworm from Another Dog?

Yes, dogs can get heartworm from another dog. Heartworm is spread by the bite of a mosquito carrying the parasite. When a mosquito bites an infected animal, the parasite is then passed on to other animals it bites.

Can Humans Get Heartworm?

Dogs are much more vulnerable to heartworm than humans and can contract the disease if they are bitten by an infected mosquito. Humans can carry the larvae of the parasite in their blood, but this is rare and usually only happens if a person is bitten by an infected mosquito after traveling to an area where dog heartworm is common.

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The only reliable way to check for heartworms in your dog is to have your veterinarian perform a diagnostic test. This test involves examining a sample of your dog’s blood under a microscope to look for the presence of microfilaria, which is the immature form of heartworms. Your veterinarian may also recommend additional tests, such as chest X-rays and EKGs, to diagnose heartworm infection.

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5 Signs Your Dog May Have Heartworm Disease

  • Coughing/Wheezing: If your dog experiences coughing or wheezing, then it is a sign that the heartworms might have caused lung inflammation and blockage in the airways.
  • Breathlessness: If your dog is having trouble breathing or is breathing faster than normal, it could be a sign of heartworm disease.
  • Loss of Appetite: If your dog has a significant decrease in appetite, it may be a sign of heartworm disease.
  • Lethargy: If your dog is more tired and listless than usual, it may be a sign of being infected with heartworms.
  • Exercise Intolerance: If your dog is no longer able to exercise as when he/she was healthy, this may be a sign of heartworm disease.

What Are The First Signs of Heartworms in Dogs?

The first signs of heartworms in dogs can vary, but the most common are a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss.

How Do Vets Test for Heartworm?

Vets use a combination of tests to detect heartworms. These include a physical exam, chest X-ray, and blood tests such as ELISA (enzyme-linked immunosorbent assay), IFA (immunofluorescent antibody), and PCR (polymerase chain reaction). During the physical exam, a vet will look for signs of heartworm disease, such as a presence of a distended abdomen or a dry cough. During the chest X-ray, a vet may be able to see an enlarged heart or the presence of fluid in the lungs. During the blood tests, the vet would look for signs of antibodies and antigens in the blood that could indicate the presence of heartworm infection.

What Months Do Dogs Need Heartworm Pills?

Most veterinarians recommend giving heartworm pills to dogs every month from April through November. This is the season when mosquitoes, which transmit the larvae responsible for heartworm, are most active. Some veterinarians may recommend year-round prevention depending on the region.

Why Do Dogs Need Heartworm Tests Before Medication?

Heartworm tests help to identify the presence of heartworms in dogs and other animals before initiating any kind of medication. Heartworms are an insidious and potentially deadly parasite, and drugs used to treat heartworm infestations can cause severe adverse reactions unless the infection is first confirmed with diagnostic testing. It is therefore crucial that any dog that may have heartworm receive a heartworm test before starting any heartworm medications.

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  1. Have your dog tested: All dogs should be tested for heartworm infection prior to initiating treatment. If the test is positive, then treatment should begin immediately.
  2. Administer oral medication: Most veterinarians will prescribe a month-long course of oral medication, such as ivermectin or milbemycin oxime. This is to kill the adult heartworms living in your dog’s body.
  3. Administer injections: If your dog’s test for heartworm is positive, your veterinarian may recommend a series of three monthly injections of a medication called Immiticide (melarsomine). This medication kills the adult worms living in the heart and pulmonary arteries of your dog.
  4. Follow a strict exercise regimen: While the medication is killing adult heartworms, it is important to limit your dog’s exercise to prevent any pieces of the dead worms from blocking the pulmonary arteries.
  5. Have your dog tested again: Two to three months after the initial treatment, your veterinarian will most likely recommend a follow-up test to make sure all of the adult worms have been eliminated.

How Is Heartworm Similar in Dogs, Humans, and Other Pets?

Heartworm in dogs, humans, and other pets is similar in that all of these animals can be infected by heartworm disease, a parasite infection caused by mosquito bites. Heartworm larvae infect the bloodstream and migrate through the heart and lungs, causing serious damage. Symptoms can include weight loss, difficulty breathing, coughing, and lethargy. If left untreated, heartworm infection can result in permanent damage and even death, but in all cases it is treatable.

How is Heartworm Different in Dogs, Humans, and Other Pets?

In dogs, heartworm infection can cause chronic heart and lung disease, and even death if left untreated. It is most commonly found in the southern and southeastern United States. Symptoms may include coughing, weight loss, exercise intolerance, and anemia. 

In humans, heartworm infection is rare but can cause fever, rash, lung inflammation, abdominal pain, and eye inflammation. 

In other pets such as cats, ferrets, and some wild animals, heartworm infection can cause weight loss, difficulty breathing, and death. It can also cause kidney, liver, and respiratory problems. 

How Does Heartworm Disease Prevention Work?

Heartworm disease is prevented by giving your pet preventive medication on a monthly basis. This medication is designed to kill any heartworm larvae that your pet may come into contact with before they can develop into adult heartworms. This prevents your pet from picking up the parasite and developing the disease.

SEE ALSO: Bloody Diarrhea In Dogs, Causes And Treatment


Q. What dogs are most at risk for heartworm?

A. Heartworm disease can affect any type of dog, but certain breeds are particularly susceptible, particularly those with long snouts like Collies, St. Bernards, and Greyhounds, as well as hunting dogs like Beagles and retrievers. Mixed-breed dogs that are not kept on regular heartworm-preventative medications are also at high risk.

Q. How long do dogs take heartworm medicine?

A. Dogs typically take heartworm medication once a month. However, the exact amount of time depends on the type of medication and the instructions provided by your veterinarian.

Q. What does dog heartworm cough sound like?

A. Dog heartworm cough is generally a dry, hacking cough that may sound similar to a person with a terrible cold or bronchitis. It is usually worse when the dog is excited or when he/she is lying down.

Q. Can dogs get heartworm in the winter?

A. Yes, dogs can still get heartworm even in the winter. Unfortunately, the cold season does not provide any protection from this disease as the mosquito, which transfers heartworm, continues to be active in warmer areas. Therefore, it’s important for owners to continue giving their pets heartworm-preventative medicine year-round.


Heartworm is a serious disease caused by parasitic worms that can affect dogs but can easily be prevented with precautionary treatments. Without treatment, the condition can worsen and can even be deadly if the worms reach the heart. Pet owners should always keep in mind that prevention is better than cure, and should take proper preventive measures, such as regular heartworm tests, along with using effective heartworm prevention treatments. If the dog is already infected with heartworm, it is important to stick to the veterinarian-recommended treatment plan to ensure a successful recovery.

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