Heartworm is passed from a host (a mosquito) to a pet host (dogs, cats and ferrets typically). It’s a pernicious parasite that lives – and reproduces – around the host’s heart, lungs and nearby blood vessels. This makes a heartworm infestation particularly dangerous, because if left untreated, it can typically kill your animal after a few months.

What are the signs my dog has heartworms?

Does he have a cough? Is he exercising less than normal? Getting winded more easily? Making abnormal, throaty sounds? Get him checked immediately. A veterinarian will take an X-ray to check his condition, handle his blood work, then prescribe him a series of injectables to kill the adult heartworms. This can be an expensive process – running in the thousands of dollars – and it’s a common problem when you adopt a dog from a shelter, so always be aware of what you’re getting into, because the disease absolutely needs to be treated.

Importantly, after you’ve treated your dog, you’ll be told to hold back on exercise. That’s because the worms are dying and they’re breaking into smaller pieces which can block the vessels around the heart. The heart is not working optimally and exercise can be a killer.

How can I prevent my dog getting heartworms?

This is the ideal solution: you can go the topical route, opt for pills or choose injectables; all of them will cost you less than $100 for the entire year.

However, if your dog is diagnosed with heartworms, this preventative medication won’t be enough. Yes, it’ll end up killing the parasite, but it’ll take longer to do so, leaving your dog at the mercy of organ damage in the process.

How does my dog get heartworms, and can they pass it on to me?

Mosquitoes carry heartworm disease. Once they’ve picked it up from a host, they then pass it on to another unwitting animal. They can’t infect a new animal immediately, however, as the heartworm goes through an incubation period in a new host.

The good news is that dogs don’t pass heartworm disease on to humans. Only mosquitoes can carry the disease – and they don’t infect us either; at least, not in 99.9% of cases. The few times a human has been infected, the parasite hasn’t been able to complete its life cycle.

One other thing: dogs don’t pass heartworm disease on to other dogs. Again: only mosquitoes can carry it.

If my dog has had treatment for heartworms in the past, can he get them again?

Yes, he can. That’s why you need to make heartworm prevention something that you carry out every year.  

While skipping a month of the medicine is probably fine, going more than two months without administering the medication will put your dog at risk again.

How long does heartworm disease take to kill a dog?

It can be less than a year – typically six or seven months. If left untreated for this stretch of time, your dog’s heart, lungs, liver and kidneys will be compromised – and your animal is likely to die.