What is heartworm disease and why should I worry about it?

Heartworm (Dirofilaria immitis) disease is a serious and potentially fatal disease that can affect dogs and cats. It is a disease that is present and endemic here in Singapore. Heartworm disease is spread by mosquitoes – when a dog or cat is bitten by a mosquito carrying heartworm larvae, the mosquito injects the larvae into the dog/cat’s subcutaneous tissues during the bite. These larvae then migrate via the bloodstream to the right side of the heart, where they start to grow to adult heartworm, which can range in size from 16 – 32 cm in length. Heartworm wreak damage in the heart and bring about respiratory difficulties as well as heart failure. In severe cases, heartworm disease can cause death.

Which animals can get heartworm?

All dogs and cats in Singapore (regardless of age) that are not on heartworm prevention are at risk of getting heartworm. Rabbits, guinea pigs and hamsters are not at risk of getting heartworm. Humans can, very rarely, be infected with heartworm.

What are the signs of heartworm disease?

Clinical signs of heartworm disease vary in severity, depending on chronicity (length of time) of infection and worm burden (number of worms present in infection). Early infection with heartworm may be undetectable, while chronic (long-standing) heartworm infection may manifest as non-specific signs such as coughing, excessive panting, exercise intolerance, lethargy, pallor (paleness) of mucous membranes, decreased appetite and/or weight loss.

In cats, clinical signs associated with Heartworm Associated Respiratory Disease (HARD) may be mistaken for feline bronchitis or feline asthma.

If your dog or cat is currently showing or has shown any of the signs mentioned above and he/she is not currently on heartworm prevention, please make an appointment with us as soon as possible to check your pet’s heartworm status.

How can I make sure my pet does not get heartworm?

If your dog/cat is less than 7 months old: Heartworm prevention can and should be instituted immediately.

If your dog/cat is more than 7 months old and/or has lapsed heartworm prevention for 7 months or more: Your pet should be tested for heartworm. If found to be negative, heartworm prevention should be instituted as soon as possible.

What does a heartworm test involve?

We will need to obtain a few drops of blood from your pet to perform a heartworm test with results available 10 – 15 minutes later. As we do not routinely carry heartworm tests for cats, please inform the clinic in advance if you wish to bring your cat in for a heartworm test.

What forms of heartworm prevention are available for my pet?

In cats, the only form of heartworm prevention labelled for such use here in Singapore is a monthly topical preventative (Revolution®). As heartworm is UNTREATABLE in cats, even though cats are less susceptible to heartworm infection, we strongly recommend starting your cat on heartworm prevention.

In dogs, several forms of heartworm prevention are available, including monthly topicals (Revolution®), monthly oral meat-flavoured tablets (Heartgard® and Interceptor®) and a yearly injectable (Proheart SR-12®).

Heartworm prevention should be given for life or for as long as your pet is here in Singapore. Most of Southeast Asia and certain regions of Australia and America are also endemic for heartworm, so it would be prudent to check if you will need to continue your pet on his/her heartworm prevention when taking him/her overseas.

Heartworm prevention should not be mistaken for other preventatives used for treatment and prevention of intestinal worms that are commonly given to dogs/cats during their vaccinations.

My pet has been diagnosed with heartworm. Is there treatment available?

In cats: There are no products approved for the use of treatment of heartworm in cats at present and many complications exist with treatment attempted with products not labelled for heartworm treatment.

In dogs: Treatment depends on the severity of the disease. In dogs with mild to moderate disease, an injectable drug is administered in 2 or more doses to kill adult heartworm present. There is a risk of dead heartworm breaking off from the heart and forming a life-threatening embolus in the lung at any point after treatment and death, paralysis, severe coughing, difficulty breathing and collapse are all possible side-effects with killing of adult heartworm. The patient may have to be hospitalised during treatment for heartworm. Damage done to the heart is only partially reversible even with treatment.

In dogs with severe heartworm disease (caval syndrome), several complications exist in addition to the presence of heartworm and death can result even with surgical treatment to remove the heartworm present in the heart.

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