Cats and Dogs
Article Rating
1 звезда2 звезды3 звезды4 звезды5 звезд

Are dogs in pain with heartworms?

Are dogs in pain with heartworms?

Unfortunately, with the warm weather we start seeing mosquitos again. They have a history of carrying diseases such as malaria, West Nile virus, and a host of other diseases. But they also carry diseases to animals. Therefore, it is vital pet parents are aware of the damage and disease they can cause their pets.

Heartworm disease is a serious disease that results in severe lung disease, heart failure, other organ damage. Left untreated it results in death in pets, mainly dogs, cats, and ferrets. When a mosquito bites an animal infected with heartworms, it sucks up the microscopic heartworm larvae. These larvae continue to develop in the mosquito, and the mosquito deposits the parasite into its next victims.

It takes about 6 to 7 months for the larvae to mature into adult heartworms. The adult heartworms mate and the females release their offspring into the dog’s bloodstream. Inside a dog, a heartworm’s lifespan is 5 to 7 years. Adult heartworms look like strands of cooked spaghetti. The male worms reach about 4 to 6 inches long and females reach about 10 to 12 inches long.

Heartworm Disease in Dogs

Symptoms of Heartworm Disease in a Dog

  • Mild persistent cough
  • Reluctance to exercise
  • Fatigue after moderate activity
  • Decreased appetite
  • Weight loss

The symptoms of heartworm disease can depend on how many heartworms are living in the dog. We call it the “worm burden”. The average worm burden in dogs is 15 worms, but that number can range from 1 to 250 worms. Symptoms can depend on how long the dog has been infected. Also, symptoms can depend on how the dog’s body is responding to the presence of the heartworms. The dog’s activity level plays a role in the severity of the disease and in when symptoms are first seen. Symptoms are not always obvious in dogs with low worm burdens, have been recently infected, or are not very active. Dogs with heavy worm burdens, have been infected for a long time, or are very active, often show obvious symptoms. There are four classes, or stages, of heartworm disease.

Stages of Heartworm

Stage 1

No symptoms or mild symptoms such as an occasional cough.

Stage 2

Mild to moderate symptoms such as an occasional cough and tiredness after moderate activity.

Stage 3

More severe symptoms such as a sickly appearance, a persistent cough, and tiredness after mild activity. Trouble breathing and signs of heart failure are common. Chest x-rays can usually show the heart.

Stage 4

There is a large mass of worms which physically blocks the blood flowing back to the heart. This stage is life-threatening and requires quick surgical removal of the heartworms. However, surgery is risky and even with surgery, most dogs in this stage die. Not all dogs with heartworm disease develop into stage 4. But if it is left untreated, heartworm disease will progress and damage the dog’s heart, lungs, liver, and kidneys, eventually causing death.

Treatment for Heartworm Disease

A veterinarian can give a dog an arsenic-containing FDA approved drug. Also, you can apply Advantage Multi for Dogs to the dog’s skin.

In any case, the treatment for heartworm disease is not easy on the dog. Treatment can be toxic to the dog’s body. It can cause serious complications, such as life-threatening blood clots to the dog’s lungs. Additionally, the treatment is expensive. It requires multiple visits to the veterinarian, blood tests, x-rays, hospitalization, and a series of injections.

The Best Treatment is Prevention!

The FDA has approved drugs to prevent heartworms in dogs. These drugs require a veterinarian’s prescription. Most products are a topical liquid applied on the skin or as an oral tablet once a month. Both chewable and non-chewable oral tablets are available. Also, a veterinarian can inject a product under the skin every 6 or 12 months. Some heartworm preventives contain other ingredients that are effective against roundworms, hookworms, fleas, ticks, and ear mites.

Testing a Dog for Heartworms

A veterinarian tests a dog’s blood to check a dog for heartworms. The test detects specific heartworm proteins. The adult female worms release these proteins into the dog’s bloodstream. In most cases, these tests can accurately detect infections with one or more adult female heartworms. The test detects heartworm proteins in a dog’s blood about 5 months after it is bitten by an infected mosquito.

Another test detects the heartworm larvae in a dog’s blood. Only adult heartworms can mate and produce larvae. Therefore, this test indicates whether or not the dog has adult heartworms. The test can detect the larvae about 6 months after infection from a mosquito. It takes about that long for the heartworms to develop from infective larvae into adults that mate and produce larvae.

Do not put your dog on any heartworm preventative medication if they have not been tested for heartworm. Heartworm preventives do not kill adult heartworms. Also, giving a heartworm preventive to a dog infected with adult heartworms may be harmful or deadly. The preventative medication may cause the larvae in the dog’s bloodstream to suddenly die. This can trigger a shock-like reaction and possibly death for the dog.

Heartworm Disease in Cats

Mosquitos can also infect cats with heartworm. However, cats are not natural hosts for heartworm. Therefore, cats are less prone to heartworm than dogs

Heartworm disease in cats is a bit different than in dogs. Heartworms in cats do not live as long. The average lifespan is only 2 to 4 years. They do not grow as long, and fewer of them mature into adults. Usually, a cat has only one or two worms. However, because of a cat’s small body size, a cat with only a few worms is still considered to be heavily infected.

In cats, it takes 7 to 8 months for infective larvae to mature into adult heartworms and produce larvae. This is about one month longer than in dogs. The presence of larvae in a cat’s bloodstream is uncommon. Only 20 percent of cats with heartworm disease have larvae in the bloodstream, compared to 80 to 90 percent of dogs with heartworm disease. Also, the presence of larvae in the bloodstream is inconsistent and short-lived in cats.

What are the Symptoms of Heartworm Disease in Cats?

  • Difficulty or labored breathing
  • Vomiting
  • Decreased activity
  • Loss of appetite
  • Weight loss
  • Convulsions.
  • Blindness.
  • Fluid in the lungs.

Not all cats with heartworm disease show symptoms. However, cats that show symptoms usually show signs of breathing difficulties due to the lung damage caused by the heartworms.

Cats typically show symptoms of heartworm disease at two different points. One is when the immature heartworms arrive in the arteries of the heart and lungs. The other is when the adult heartworms die. Cats with heartworm disease rarely show signs of heart failure. However, some infected cats die suddenly from heartworm disease without ever showing signs of being sick. And in some cases, cats have been able to rid themselves of heartworms without ever having any symptoms.

It is harder to detect heartworm infections in cats than in dogs. Veterinarians generally use two types of blood tests in combination to check a cat for heartworms. However, negative test results do not rule out heartworm infection. Positive test results may or may not mean that there is an active heartworm infection. A veterinarian uses the results of both blood tests, along with the cat’s symptoms and the results of other tests such as x-rays and an ultrasound of the heart, to determine if a cat has heartworm disease.

Infection in Cats

After an infected mosquito bites a cat, the immature heartworms arrive in the heart and lung arteries in about 3 to 4 months. Many of these immature heartworms die, causing a strong inflammatory response in the cat’s lungs. We call this response heartworm associated respiratory disease (HARD). It refers to breathing difficulties, such as trouble breathing, increased breathing rate, and cough. It may be difficult to distinguish HARD from feline asthma or feline bronchitis.

When the adult heartworms die, they release toxins into the cat’s bloodstream which causes lung damage, leading to respiratory problems or sudden death. Even the death of one worm can be fatal for a cat.

There is no FDA-approved drug to treat heartworm disease in cats, although symptoms may be managed with medications. If a veterinarian can detect heartworms by ultrasound, surgical removal of adult heartworms may be an option. But surgery is risky. And if the heartworms are not removed intact, there can be potentially serious complications, such as shock and death.

Should Cats Be Tested for Heartworms?

We recommend that cats be tested for heartworms before starting heartworm prevention, although this pre-testing is less useful than in dogs. Talk to your veterinarian about testing your cat for heartworms.

Heartworm Disease in Ferrets

Ferrets can also get heartworms from the bite of an infected mosquito. They are extremely susceptible to heartworm disease and are at risk for the disease even if they are indoor pets. Ferrets are similar to dogs in their susceptibility to heartworm infections, but their symptoms are more similar to those seen in cats.

Infected ferrets typically have low worm burdens. A test shows larvae are seen in the bloodstream in only 50 to 60 percent of ferrets with heartworm disease.

Symptoms of heartworm disease in ferrets

  • Decreased activity
  • Coughing
  • Trouble breathing
  • Overall weakness
  • Heart failure can occur in severe cases.

Based on a ferret’s symptoms, a veterinarian may perform chest x-rays and an ultrasound of the heart to determine if it has heartworm disease. Blood tests to detect heartworm infections in ferrets are generally unreliable.

Treatment for Ferrets

Unfortunately, no drugs are FDA-approved to treat heartworm disease in ferrets. And only one drug, Advantage Multi for Cats is approved to prevent heartworms in ferrets. It is a topical solution that is applied monthly. Besides preventing heartworms, Advantage Multi for Cats also treats flea infestations on ferrets by killing adult fleas. We recommend year-round prevention medication for all ferrets.


Only a veterinarian can prescribe heartworm treatment and preventative treatment. Heartworm preventive medication will not kill existing adult worms. Therefore, we cannot overstress that PREVENTION is the best treatment for heartworm. It’s much easier (and less expensive) to prevent heartworm than to treat it after the fact. Contact us if you have any questions or need to schedule your pet for a heartworm test or preventative medication.

Sincerely, Stacey Funderburk D.V.M.

Heartworm Testing


Yearly heartworm testing is strongly recommended in all dogs. The blood test can be performed at your veterinarian’s office and will test for the presence of heartworms and other tick-borne diseases such as Lyme’s disease. Once we are sure your dog is free of heartworms a monthly preventative medication will be dispensed. This ensures your dog will remain heartworm-free during the summer and fall months.

What are the symptoms of heartworms in a dog?

Clinical signs vary depending on the type and number of heartworms present in the animal’s body. Clinical signs can include: asymptomatic (no clinical signs), coughing, exercise intolerance, nose bleeds, pot-bellied appearance, difficulty breathing, collapse, shock, and/or death.

How do dogs get heartworm?

Dogs acquire this infection through mosquito bites, as mosquitoes readily pick up larval heartworms from infected dogs and carry them to new dogs.

What are the treatment options for heartworms?

Stabilization of the patient. Some dogs will require exercise restriction prior to treatment. If the dog has heart failure, this will need to be controlled. Some dogs will need anti-inflammatory doses of steroids to control the inflammation that stems from the presence of worms.

Heartworm treatment can last at least a couple of months, thus it is important to prevent the immature worms from developing into adults. Immature worms can be killed by administering monthly heartworm preventive products. The American Heartworm Society recommends one to three months of a preventive prior to treating the adult worms.

The only product currently available for the treatment of adult heartworms is melarsomine dihydrochloride (immiticide). During treatment, the patient receives an intramuscular injection deep in the lower back muscles. This is a painful injection and it is common for the patient to be quite sore at home afterwards. Pain medication may be needed. The site may form an abscess, which requires warm compresses and possibly antibiotics. Approximately 30% of dogs experience some sort of injection site reaction that resolves in one to four weeks. Some dogs develop a permanent firm lump at the injection site.

After the treatment, the patient must be strictly confined for one month following the final treatment, no walks and no running around. The dog must live the indoor life. Exercise increases the heart rate and oxygen demand and we need the heart to last during this recovery period.

Why is recovery and heartworm treatment challenging?

Treatment of heartworm can be quite challenging, as it spans over several months, is very expensive, requires strict exercise restriction and can be life-threatening to the patient. Treatment involves using very harsh arsenic-based drug to kill the adult heartworms. This medication is painful to administer and can lead to injection site reactions in some patients. This killing of the heartworms can also lead to anaphylactic shock in some patients, which in some cases can lead to death. The most critical time period is 7 to 10 days following treatment, but these signs can occur anytime in the following month.

Veterinarian with owner and dog

From Our Blog

Vaccines and Why My Pet Should Get Them?

Whether it be humans or pets we all know that immunizing against diseases is the best tool for preventive medicine.

Heartworm Disease

The American Heartworm Society website has excellent and detailed information on this debilitating and often fatal disease in dogs. Our discussion here will focus on the dog’s disease prevention, and treatment. Cats can get heartworm, but do not suffer fatalities like the dogs. We will provide prevention and treatment to dogs until research deems it necessary and prudent to do so for cats in our area.
The protocols used here are tailored to the individual dog’s disease state, lifestyle and personality. This is not a one size fits all program. Prevention is offered after appropriate testing and monitoring and can be in the form of monthly pills, liquid, or a twice a year injection. Treatment can be a short, fairly inexpensive process, or it can be a long, step by step expensive series of medications. It is always best to prevent this disease in the first place.
There is no state that is immune to this disease nor is there a time of year when it
is safe to not be on prevention medication.

Wild canids like the coyote also carry the disease and serve as a permanent reservoir of infection for our dogs.


Heartworms are thread-like worms that can be 6 to 10 inches long. They live inside your dog’s heart near or into the arteries that feed the lungs. Adult worms will reproduce and lay thousands of microscopic baby worms that circulate throughout the dog’s body. Mosquitos feed on your dog’s blood and suck up these infant worms and the worms go through a developmental stage inside the mosquito. The next time the mosquito feeds on your dog or your neighbors dog or a visitor’s dog, the new teenage form of heartworm is passed back into the tissue where it matures some more. Six months later the young adult has migrated to the heart where it starts reproducing and the process repeats. This cycle occurs over and over through the life of your dog and you would never know he was infected until one of two things occurs. He is blood tested on a routine pre-prevention exam, or he shows signs of heart and or lung disease and is then blood tested. Adult heartworms have been known to survive inside a dog’s heart for 7 years before they die on their own. Your dog does not spit them up, poop them out, or dissolve them on his own. The adult worms will live a long, productive life inside your dog’s heart wreaking havoc on his heart and lungs.


Early symptoms can be as slight as a mild cough or as terrifying as sudden death. That’s the problem with this disease. It will cause weight loss, lack of appetite, distended abdomen (pot-belly), passing out episodes, dull coat, lack of energy, lung disease, coughing, loss of alertness, and depression as the disease goes undetected and untreated.

Most heartworm infections go undetected since there are usually no symptoms early on in the disease process. Several factors can cause symptoms to be hidden (occult) which are typical in many infections. If there are only a few adult worms in the heart and they are not clogging the flow of blood to the lung, or the dog may be very sedentary and you don’t notice lethargy or exercise intolerance. Your dog may have been in heartworm territory in another state while on vacation with you and became infected too.


With sudden death as a symptom. preventing this disease in the first place is paramount! It is critical, however, to test for the presence of the adult worms before starting a prevention program. Not all veterinarians use the same protocol for prevention. Our protocol is based on logical conclusions given what we know about this parasite: The testing at the correct time is critical to keeping your dog protected. Knowing that it takes 6 months from the time an infected mosquito bites your dog until an adult worm can be detected means that dogs less than 6-7 months old do not need to be tested before starting prevention. All dogs older than 6-7 months must first be tested before starting prevention. Since the test only detects the presence of the adult worm in the heart there will be another test 6 months after the first initial test to confirm that there were no immature worms that grew up into adults during that timeframe. The prevention medication only kills the infant form of the parasite and it will not kill the parasite once it is 4 months old. Testing must be a part of the prevention program or you can miss infections and allow them to do damage to your dog.

There are at least 3 good reasons to repeat testing every 2 years:

  1. a dog can vomit up the prevention medication without you knowing it
  2. you can miss a month of prevention or give the wrong dose due to weight changes of your dog
  3. the manufacturer of the prevention drug may make an error in dosing

These are all reasons why we adhere to a strict protocol that requires testing of dogs over 6 months old and retesting 6 months later and then retesting every 2 years or as needed if doses are missed.

Monthly prevention can be a single ingredient to kill only the infant heartworm, or it can be a combination of that drug and two others that kill intestinal parasites too. We also have an injectable drug that is only given every 6 months, but it only kills the infant form of heartworm. You can decide which method works best for your dog and your lifestyle. whatever you choose, your dog should be on preventive all year long.


Although heartworm disease can be fatal, and treatment can be risky, the condition is nearly always curable. Treatment requires careful medical management and strict confinement and rest at home. After the positive test you will be counseled on where to go from there. Some owners decide not to treat due to a variety of reasons like, the dog is suffering from another more serious illness, the dog will not likely survive the treatment due to the severity of disease, or treatment will put the family in financial hardship. Once treatment is authorized, the process to evaluate further can begin. Blood tests to assess risk and possibly X-rays of the chest to evaluate lung and or heart damage are advised at this time. Your dog must be able to handle the arsenic-based drug used to kill the adult worms. He must also deal with the dying worms and be able to dissolve them in his bloodstream during the recovery period.
If we detect existing disease or compromise of any other organ system, then we will likely treat that disease as much as
possible before starting the arsenic compound.

Veterinarians also differ here in the treatment plan. There is no way to know how many worms there are or how they are situated in your dog’s heart, so our philosophy is to treat all patients as if they are at high risk. That entails more of a slow kill of the worms
with 3 injections rather than the faster kill done with 2 injections.

Some dogs are pre-treated with steroids, antibiotics, and heart drugs for weeks before the injections start. The dog will also be started on the first monthly dose of prevention during this time. We will watch your dog for 8 hours during the initial exposure to the prevention since some dogs will experience an allergic-type reaction to the dying infant form of the parasite
and need emergency medical treatments.

Immiticide is the name of the arsenic-based drug that is used to kill the adult worms. It is given by injection deep into the back muscle. An anti-inflammatory drug can be given at this time too and for the next few days for the swelling and pain that usually results. It seems to be a bit like how we feel after we get a tetanus shot. Be prepared for your dog to be a bit grumpy and sore.

It is critical for your dog to rest and avoid vigorous activity for 30 days after each of the 3 injections. This is the time when the dog’s body is dealing with disposing of the dead and dying worms. If a large chunk of dead worm dislodges from the heart lining and is pumped out into the lungs it will act like a blood clot. A clot to the lung will cause pain, shortness of breath, and lack of circulation to the lungs leading to loss of oxygen and possible death. We will test your dog’s blood 6 months later to make sure every
last worm died during our treatment.

  1. Pretreat with steroid, antibiotic, and prevention medication at positive test outcome.
  2. Determine best time to start Immiticide injection.
  3. STRICT rest for 30 days after first injection
  4. Give 2nd injection 30 days from the first and decide if the 3rd injection is given
  5. either 24 hours later or 30 days later.
  6. Continue STRICT rest for 30 days after each injection.
  7. Maintain monthly prevention and supportive medication.
  8. Retest 6 months after last treatment shot


BUY A 12 MOS SUPPLY FROM US OR VETSOURCE (our online pharmacy)

Link to main publication