No doubt you’ve heard the old saying “prevention is better than cure”. Never has this saying been more true than for heartworm infections in pets. Preventing heartworm infection is cheap and can be as easy as giving your pet a monthly tablet or yearly injection. Treating a heartworm infection on the other hand, can be costly, potentially life-threatening and may involve surgery to remove worms directly from your pets heart. Not a nice thought.
This ultimate guide to heartworms will cover how your pet contracts heartworms, what you can do to prevent heartworm infection in your pet and a bit about what treating a heartworm infection can involve. Towards the bottom of the page, there is also a handy comparison chart so you can easily see which medicines protect your pet from heartworm, and if they treat for other parasites as well. You can use the links below to jump between the headings for easy navigation.
I Didn't Think Heartworm Disease Was a Problem Anymore?
Heartworm disease used to be a huge problem for pet owners. That was until the yearly heartworm injection became available. Since then, rates of heartworm infection in pets dropped dramatically.
But in 2016, a study of pets in Queensland and New South Wales found an increase in heartworm infections and discovered that up to 20% of dogs could be infected with heartworms. An Australian Dog Owner Survey conducted in 2015 found that owners were confused about the symptoms of heartworm disease, and worryingly, many owners were often late with their monthly doses, leaving their dogs exposed to heartworm infection. In dogs that have not been given a heartworm preventative, up to 80% can be infected with heartworm!
How Does Heartworm Spread?
Heartworm is spread by up to 70 different types of mosquitoes (not that we needed another reason not to like mozzies!). Heartworm cannot be transmitted directly from cat-to-cat or dog-to-dog. Transmission via mosquito is the only method of infection.
Heartworm is transmitted when an infected animal is bitten by a mosquito, which sucks up the miniscule heartworm larvae in the blood. The larvae live in the gut of the mosquito for up to 30 days, and when that mosquito bites another animal, it injects these larvae into their bloodstream. The larvae circulate in your pets body, eventually making their way to the heart and blood vessels of the lungs where they spend around six to seven months growing, reaching up to 30cm in length.
The worms can live in the heart and blood vessels of the lungs for up to seven years, and dogs can show no signs of infection for up to five years while the worms grow.
Recent studies have revealed that the rate of heartworm disease in cats is higher than first thought. Cats are less likely to have as many worms present as dogs and it is also much harder to diagnose and treat heartworm disease in cats, than it is in dogs. The same medications that are used to treat heartworm disease in dogs cannot be used in cats and the test used to diagnose heartworm in dogs doesn’t work for cats either.
Is My Pet At Risk?
Given that heartworm can only be transmitted by mosquitoes, the rate of infection is much higher in places with a large mosquito population and warm climate. In Australia, it is recommended that a heartworm preventative is given all year round. In some countries, pets only need to be given a heartworm preventative during mosquito season.
Foxes, dingoes, ferrets and wild dogs are the most common carriers of heartworm. In the Melbourne region, up to 7% of foxes were found to have heartworm. In the Sydney area, 9% of foxes were found to be infected. A study from 2016 found that over 70% of wild dingoes tested positive for heartworm.
Symptoms of Heartworm Disease in Dogs
It can take up to five years for a dog to show symptoms of heartworm infection. By this time, it is likely that your dog already has hundreds of heartworms living in their heart or the blood vessels of their lungs. When the worms have grown large, they can restrict the flow of blood in the heart and blood vessels of the lungs, putting the heart under immense strain, and causing it to become enlarged. The reduced blood supply from the heart can damage other organs in the dog’s body.
The early symptoms of heartworm infection in dogs can include the following:
- A dry, persistent cough
- Lack of energy or tiring easily
- Shortness of breath or difficulty breathing
In the later stages of infection, the following symptoms can appear:
- Weight loss
- Lack of appetite
- Enlarged abdomen due to fluid build up
- Increased thirst (from kidney disease)
- Bleeding from the nose
- Sudden collapse, fainting or seizures
If a dog has a severe heartworm infection, they may suffer permanent damage to their heart or lungs. Left untreated, heartworm disease is fatal and sudden death can occur without any prior symptoms.
Symptoms of Heartworm Disease in Cats
With their smaller hearts, the presence of only one or two adult heartworms can cause problems in cats. Early symptoms of heartworm disease in cats can often be confused for feline asthma or feline bronchitis.
The symptoms of heartworm infection in cats can include:
- Coughing, gagging or wheezing
- Difficulty breathing
- Increased respiratory rate
- Decreased appetite
- Weight loss
- Vomiting (of food or blood)
- Decreased activity levels
Some rarer symptoms of heartworm infections in cats includes:
- Difficulty walking
- Fluid build up in the abdomen
Cats with heartworm disease do not often have symptoms of heart failure. In an acute case of heartworm disease, a cat may pass away suddenly.
How Is Heartworm Disease Detected?
In both cats and dogs, blood tests as well as ultrasounds and x-rays are required to diagnose heartworm disease. Your veterinarian will consider the results of any tests performed, along with any symptoms your pet may present with, before making a diagnosis of heartworm disease.
How is Heartworm Disease Treated?
Several factors will determine the type of treatment that your veterinarian will recommend if your pet has been diagnosed with heartworm disease.
- The stage of infection (how many worms are present, where and in what life stage?)
- How healthy your dog is (are they old, do they have any other health concerns?)
- Whether or not you are able to “cage-rest” your dog for up to 8 weeks (this means restricting your dog to zero exercise!)
- Cost (treatment can be very expensive!)
The most common treatment is a series of injections accompanied with antibiotics, and sometimes other medication and fluids. For dogs with a very severe heartworm infection, surgical removal of worms from the heart may be necessary. All treatments for heartworm infection carry some level of risk, and in severe infections, even with treatment, the dog may still pass away.
Cats cannot be treated for heartworm infection as easily as dogs, as the medication used to treat an infection in dogs is toxic in cats. Prevention is your only hope in preventing heartworm infection in cats. Some medications to help manage the symptoms of infection can be given to cats, and removal of the worms from the heart during surgery can be attempted also. Cats must also be confined and their exercise restricted to avoid putting any unnecessary strain on their heart.
Preventing Heartworm Disease in Your Pet
Prevention is the best form of heartworm control, and in Australia, it is recommended that cats and dogs receive heartworm preventatives all year round starting from when they are a few weeks old. Compared to treating a heartworm infection, preventing heartworm disease is much cheaper and there are several products on the market for both cats and dogs that will protect them from heartworm, as well as many other parasites.
You can use our heartworm preventative comparison chart below to compare all of the products that protect your dog or cat from heartworm and see what other nasties they will protect your pet against. Some heartworm preventative products do require you to have your pet tested for heartworm before commencing treatment. This is because if there are already worms present in your pet, treating them with certain medications can kill the worms and this can cause blockages or other issues in your pet's heart and blood vessels.
Heartworm Preventative Product Comparison Chart for Dogs
Heartworm Preventative Product Comparison Chart for Cats
View all heartworm products for dogs here
View all heartworm products for cats here