How Long Can a Dog Live with Heartworms?

heartworm prevention for dogs
iStock.com/Wild spirit shoot

Written by Em Casalena

Updated: October 5, 2023

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In the United States and many other countries worldwide, heartworm illness in pets is a serious and sometimes deadly condition. Heartworm illness affects dogs and is brought on by foot-long worms also known as heartworms. These worms reside in the heart, lungs, and blood arteries. These worms can cause everything from heart failure to severe lung disease to overall bodily harm if not treated.

Heartworms can thrive in other animal species, such as wolves, coyotes, foxes, cats, ferrets, and, in rare cases, humans. Wild animals like coyotes are major disease vectors for heartworm because they sometimes reside close to residential areas.

If your furry friend has been given a heartworm diagnosis, you may be wondering how long they can live with heartworms. Many dogs receive a late diagnosis of the disease, when treatment may not work quite as well. In this guide, we’ll break down what heartworms are and what they do. We’ll also explore how long the average dog can live with heartworms.

What Causes Heartworms?

Dirofilaria immitis is a blood-borne parasite that causes heartworm illness. It is a dangerous condition with a high mortality rate. Infected dogs have adult heartworms in their hearts, pulmonary arteries, and nearby big blood vessels. Worms can occasionally be discovered in other areas of the circulatory system. Female worms are an eighth-inch broad and six to 14 inches long. The size of males is around half that of females.

When diagnosed, a dog can have as many as 300 worms present. Heartworms can survive in a pet’s body for up to five years. Millions of microfilariae, the female heartworm’s offspring, are produced during this period. These microfilariae mostly inhabit the tiny blood arteries.

Dirofilaria immitis or heartworm in a petri dish of dog's blood.

Dirofilaria immitis or heartworm (pictured) is caused by a parasite that stays in the heart chambers and even lungs of dogs.

How Does Heartworm Spread in Dogs?

A major spreader of heartworm is, surprisingly, mosquitos. The illness is not transmitted directly from dog to dog. That’s because the mosquito is an intermediary host in the transmission process. Hence, the disease’s spread aligns with mosquito season. In many areas of the United States, mosquito season can persist all year. The prevalence of heartworm disease in any particular location is closely connected with the number of affected dogs and the length of the mosquito season.

How Long Can a Dog Live with Heartworms?

By the time they are diagnosed, many dogs already have advanced heartworm disease. The heart, lungs, blood vessels, kidneys, and liver can sustain significant harm as a result of the heartworms’ protracted presence. 

Occasionally, instances may be so severe that treating organ damage and providing the dog with comfort is preferable to risking the side effects of heartworm treatment. The lifespan of a dog in this condition is most likely limited to a few weeks or a few months. Your vet will guide you on the best course of action for treating your dog depending on the severity of their infection.

Dogs can live for at least six to seven months after becoming infected with heartworms. This is because it takes that long for adult heartworms to grow. However, determining the exact date of infection is challenging. If the illness is treated in stages one or two, your dog should recover and have a normal, healthy life. While treating patients in stages three or four, there is a considerable risk of organ damage. This might result in heart failure or lung and respiratory conditions. Your dog’s life expectancy would be shortened by this.

Can Dogs Survive Heartworm Disease Without Treatment?

In general, no. However, it is certainly possible. If a dog’s heartworm infection does not progress to stage four, it may still live. These are the worst-case scenarios. Regardless of the stage of infection, your dog is at, heartworm illness is a dangerous ailment. It still has to be treated effectively to end your pup’s suffering. If this situation is ignored, especially for an extended length of time, your dog won’t live and will undoubtedly suffer.

Dogs with heartworm disease will eventually go through four phases of infection. They have symptoms that can be anything from mildly unpleasant to lethal. Caval syndrome, the last stage of heartworm infection, is particularly fatal. It is a disease when enormous swarms of worms begin obstructing the blood supply to the heart. When a dog reaches this stage, the prospects of survival are very slim. Surgery is usually the only option for treatment. Even surgery is not always successful, and the possibility of death is high. Only after surgically removing the adult heartworms obstructing the blood flow can dogs with Caval syndrome be saved. But unfortunately, it happens often for infected dogs to pass away during or right after surgery.

Dog getting vaccination

Dogs (pictured) should always be given treatment once a heartworm diagnosis has been given by a vet.

How Long Can a Dog Live Without Heartworm Treatment?

A dog can live at least six to seven months from the date of infection. The length of time a dog can survive without treatment depends on how bad the problem is. That being said, the solution is more intricate. 

When a dog is bitten by a mosquito carrying tiny heartworm larvae, the larvae enter the dog’s bloodstream through the bite site and cause heartworm disease. Once this occurs, it may take the larvae six to seven months to mature into adult heartworms. When they reach adulthood, heartworms reproduce with one another. This causes the females to release additional young heartworms into your dog’s blood circulation. Unfortunately, this leads to the disease spreading quickly and brings on more symptoms.

The illness comprises four stages, as was already mentioned, each with a unique set of symptoms and degrees of severity. We can expect that the majority of dogs can live for at least six months after infection. This is because the majority of symptoms don’t appear until the heartworms are fully developed. Nevertheless, when the adult heartworms have finished their life cycle and have reproduced, the dog becomes more susceptible to Caval syndrome and its fatal symptoms.

As a result, it can be said that your dog will survive the first six months of the infection before things start to get worse. Following the early phase, the disease only takes a few weeks to a month to reach its terminal stage, at which point your dog will quickly degenerate and regretfully pass away. For the greatest results, heartworm disease must be treated as soon as possible.

Heartworm Disease Treatments for Dogs

Although fatalities are uncommon, treating dogs for heartworm carries considerable risk. In the past, the medication used to treat heartworm illness contained significant amounts of arsenic. This usually resulted in severe side effects. More than 95% of dogs with heartworms can be successfully treated with a newer medication that has fewer negative effects.

Therapy for Heartworm Larvae

Your dog will first take medication to destroy microfilariae or heartworm larvae. This is done before receiving the medication that is used to eliminate adult heartworms. On the day that this medicine is given, your dog might need to stay in the hospital for monitoring. This might happen either before or after the injections for adult heartworms. Your dog will begin taking a heartworm preventive after treatment. Prior to melarsomine therapy, which we’ll discuss in the following section, many dogs may also receive the antibiotic doxycycline to stave against potential infection with bacteria that live inside the heartworm larvae.

Heartworm medication for adults

Melarsomine, an injectable medication, is used to destroy adult heartworms. Adult heartworms are killed by melarsomine in the heart and surrounding blood vessels. A series of injections are used to give this medication. The precise injection schedule will be decided by your vet based on the health of your dog. The majority of dogs have a first injection, a month of rest, and then two further injections spaced 24 hours apart. As melarsomine can induce muscular discomfort, painkillers are frequently given to dogs as well.

During therapy, complete rest is necessary. During the span of a few days, the adult worms die off and begin to decompose. In the lungs, where they lodge in the tiny blood vessels after fragmenting, they are finally reabsorbed by the dog’s body. The majority of post-treatment difficulties are brought on by these pieces of deceased heartworms. Their resorption might take many weeks to months. Your dog must be kept as relaxed and stress-free as possible during this potentially dangerous time. Regular activity cannot begin until one month after the final injection of heartworm therapy.

Each injection’s first week is crucial since the worms are dying at this time. Many dogs with severe infections continue to cough for seven to eight weeks following therapy. If your dog experiences a strong response in the weeks after the initial treatment, prompt treatment is crucial. However, such reactions are uncommon. If your dog exhibits lethargy, fever, intense coughing, shortness of breath, blood in the cough, or lack of appetite, call your veterinarian right away. Anti-inflammatory drugs, antibiotics, cage rest, supportive care, and intravenous fluids are the most effective treatments in these circumstances.

What is the Survival Rate for Dogs with Heartworm?

If given the right care and medication, the majority of dogs can recover from heartworm disease and enjoy a healthy, long life. However, the survival rate for dogs with heartworm infection is incredibly poor in the absence of therapy or treatment. This is particularly so if it has reached the terminal stage.

As individual dogs’ worm loads and stages vary, it’s challenging to provide a precise number. We can, however, state that the dog will most likely pass away without surgical intervention if the condition has progressed to Caval syndrome.

How to Prevent Heartworms in Dogs

Your veterinarian can give your dog a heartworm prevention drug that is FDA-approved. Depending on your veterinarian’s advice, preventative treatments can include monthly oral pills or injections given every six to 12 months. Fortunately, some of these treatments also protect against other parasites including hookworms and roundworms.

A heartworm prevention regimen is essential since the illness might return to infect your dog even after good treatment. Taking precautions to ensure this doesn’t happen again is always a good idea. Your dog testing positive once more is the last thing you want to see after this horrible experience. In fact, when a dog contracts heartworms, veterinarians advise owners to use heartworm preventive treatments going forward for the rest of the dog’s life.

If your beloved pup is suffering from heartworm, it is recommended to seek out treatment as quickly as possible. While treatment can occasionally be risky for dogs, going without treatment is significantly worse. Prevention is key!

What are the Symptoms of Heartworm Infection in Dogs?

heartworm prevention for dogs

One of the first signs your dog may be infected with heartworm is a mild, persistent cough.

Quite often, people are unable to tell right away if their dog is infected with the heartworm parasite. While you may seek treatment for them as soon as you detect it, if not treated close to the beginning of the infection, your dog’s survival rate will decrease. It can take months and even years, to detect any symptoms. If you are worried that you may not discover it in time, here are a few signs to look out for:

  • Difficulty Breathing – in addition to a cough, your dog may develop respiratory issues that cause breathing to increase.
  • Lethargic – if your dog doesn’t wish to participate in its favorite activities, like walking or playing fetch, this may be a sign they have heartworms.
  • Mild Persistent Cough – this is one of the first signs your dog may be infected. Should your dog develop a dry, persistent cough, you should see a vet.
  • Swollen Belly – heartworm can cause a dog to have heart failure and an indicator of this infection is a belly that becomes swollen from fluid.
  • Weight Loss – due to a decrease in appetite, your dog may lose weight.

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About the Author

Em Casalena is a writer at A-Z Animals where their primary focus is on plants, gardening, and sustainability. Em has been writing and researching about plants for nearly a decade and is a proud Southwest Institute of Healing Arts graduate and certified Urban Farming instructor. Em is a resident of Arizona and enjoys learning about eco-conscious living, thrifting at local shops, and caring for their Siamese cat Vladimir.

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