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Heartworm FAQs

How does a pet get heartworm?

Heartworms can only be transmitted from host to host in one way: by the bite of an infected mosquito. Mosquitos pick up heartworm larvae by feeding on an infected host – this includes not only dogs, cats, and ferrets, but wild animals such as wolves, foxes and coyotes. These larvae develop within the mosquito to the infective stage and are then transferred to a new host as the mosquito feeds.

Can cats get heartworm?

Cats are just as much at risk of being bitten by an infected mosquito. Once bitten, their chance of the heartworms maturing and multiplying is somewhat lower than dogs, as cats are not natural hosts for the parasite. However, a cat’s health can be seriously impacted by just one or two adult heartworms. Keeping your cat indoors does not guarantee that they will not be infected by heartworms, as mosquitoes can easily get inside. In fact, up to a third of cats with heartworm disease are indoor cats. As there is no treatment available for heartworms in cats, preventative action is key to protecting your cat.

Are heartworms contagious?

The good news is that heartworms are not directly contagious. Heartworm larvae can only be transmitted by mosquitoes - they are not transferred from pet to pet by contact, coughing or eating infected meat. Nor can heartworms be passed from mother to their litter. A heartworm-positive pet does not need to be isolated, but any other pets will still be at risk of contracting heartworms through mosquito bites.

How do heartworm preventatives work?

Despite the name ‘preventative’, heartworm medications cannot stop mosquitoes from transferring heartworm larvae to your dog or cat. What the medication does is eliminate any larvae that have entered the bloodstream in the 30 days previous, preventing them from developing into adult worms. Heartworm preventatives do not remain in the bloodstream and have no effect on new larvae that may be transmitted. This is why it is so important to maintain a regular schedule for your pet’s medication.

Most heartworm preventatives also treat other external and internal parasites, making health care more convenient and affordable for pet owners. Popular products include Advantage Multi or Revolution, which also treat fleas and intestinal worms and mites.

Do I need to test for heartworm before starting preventatives?

Yes, due to the way that heartworm medications work, prior testing is necessary. Heartworm preventatives work by killing off microscopic larvae known as microfilariae before they can mature. These preventatives are not used to eliminate adult heartworm. By giving heartworm preventatives to a heartworm-positive animal (dogs in particular) you run the risk of causing an anaphylactic reaction, which may result in sudden death.

My dog/cat is on heartworm medication – do they still need to be tested?

Yes, even if you administer a monthly medication, your vet will recommend you still have your pet tested regularly for heartworm. It is possible for your dog or cat to spit out or vomit tablets or chewable, or to rub off topical treatments. And although medicated heartworm preventatives provide the best available protection against the development of heartworm disease, no measure is 100% effective.

Can I give heartworm preventatives to my pregnant or nursing pet?

Yes, there are a number of heartworm preventatives that are safe for use with pregnant or lactating dogs and cats. These include Heartgard (dogs only) and Revolution (dogs and cats). As with all medications, it is important that you carefully read and adhere to the included instructions. If you can any concerns about the suitability a medication for your pet, please consult your veterinarian.

Are puppies and kittens immune to heartworm?

Unfortunately, puppies and kittens are just as susceptible to infection with heartworm as adult animals. Mothers cannot pass on immunity to their young, nor can they transfer the effects of heartworm preventatives by nursing. Puppies and kittens should be started on regular medications as soon as they reach the age as noted by the particular medication you select, and by 8 weeks at the latest. Animals younger than 6 months do not require prior testing - as the worms themselves take 6 months to develop. Many medications available are designed to be safe for animals as young 6-8 weeks, such as Revolution.

When should my pet be started on heartworm medication?

It is recommended that puppies and kittens are started on heartworm preventatives by 8 weeks of age at the latest, and earlier if the particular product allows. Dogs or cats under 6 months of age can be given preventative medication without first being tested for existing heartworm.

Some combination medications may not be suitable for young dogs or cats, even if they include a heartworm preventative. Please read the product information carefully and consult your vet it if you have any concerns.

What happens if I miss a dose?

Maintaining a regular dosing schedule is vital to ensuring your heartworm medication is effective. If the dose is less than a week late, give the missed dose immediately and resume a regular dosing schedule. If the dose is more than a week late, contact your vet. Giving heartworm preventatives to an animal that has been infected with heartworm can be dangerous, particularly for dogs. Depending on how late the dose is, your vet may advise resuming preventative medication, but you will also need to schedule a heartworm test for your dog or cat.

Is there a vaccine for heartworm?

No, at this point there is no vaccine that will provide immunity from heartworm. The only option is to administer regular preventative medication. If you stop this medication your dog or cat will no longer be protected from developing heartworm disease. Preventative medications are most commonly available as topical or oral applications, to be administered once a month. In some countries, a 6-month or 12-month injection is available for dogs only.

What are the symptoms of heartworm?

In dogs, the severity of symptoms is usually determined by the number and size of the adult heartworms in the body. Early signs include coughing, lethargy, and weight loss. As the disease progressed your dog may experience breathing problems and fainting.

Cats are less likely to display symptoms of the disease, but unlike dogs, they can be affected by just one or two heartworms. Symptoms in cats include breathing problems, vomiting, lethargy and loss of appetite.

It is important to remember that both dog and cats may be asymptomatic during the early stages of heartworm. This is why regular testing, even if your pet is taking regular medication, is so important.

Can heartworm disease be treated?

If a dog develops heartworm disease, there are treatment options available, though it should be noted they are very involved, expensive and potentially dangerous. Treatment will consist of a series of injections administered by your vet, often spread out over a number of months, which will kill the adult heartworm. As the heartworms die and decompose, the fragments can cause blockages in a dog’s blood vessels, so your dog will need to be confined to avoid excessive movement. Your vet may also recommend treatment to alleviate the symptoms of the disease.

There is currently no available treatment for cats, as the drugs used to eliminate heartworms in dogs are dangerous for cats. For cats, the only option is to treat the symptoms of heartworm and endeavor to keep your cat healthy until the worms die off naturally – which can take up to 2-4 years. During this time your vet may need to prescribe steroids for inflammation in the heart and lungs, medication for breathing issues, and provide general nursing care.

Can humans get heartworm?

As we all know, humans receive just as many mosquito bites as other animals, if not more. Thankfully, humans are not natural hosts for heartworm and the larvae are rarely transferred into the bloodstream, even when bitten by an infected mosquito. On the rare cases that these larvae do transfer to humans, they do not develop into adult worms and do not cause the same health issues that they do in dogs or cats.

Heartworm FAQs

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