A Pet Owner’s Guide to Heartworm Risks and Prevention

While April marks Heartworm Awareness Month, pets in Singapore face a year-round risk due to the  humid climate, which is ideal for mosquitoes - the sole carriers of heartworm disease - to thrive. In fact, the disease is highly endemic in Singapore, with studies suggesting that up to 1 in 7 pets not on preventive care may be at risk¹.
 

Often referred to as a “silent killer,” heartworm disease rarely shows symptoms in its early stages. Unfortunately, this also means that many pet owners only discover the problem once the condition has progressed to a severe, potentially deadly stage of disease.

Heartworm disease is caused by the parasitic roundworm Dirofilaria immitis¹, that’s transmitted through the bite of an infected mosquito. Once inside the body, microscopic larvae travel through the bloodstream toward the heart, lungs and blood vessels where they develop over several months into adult worms that can grow up to 30 cm long².
 

Although both dogs and cats can be infected, the disease affects them differently:

In Dogs: As natural hosts, dogs allow the worms to mature, mate, and multiply in affected areas. Over time, large numbers of worms can accumulate, causing blockages, organ damage, and potentially even heart failure.

In Cats: Cats are atypical hosts, and while fewer worms survive, even a small number can be dangerous, as the immune response may trigger Heartworm-Associated Respiratory Disease (HARD)³, leading to severe lung inflammation, respiratory distress, or sudden death.

Heartworm disease spreads exclusively through mosquito bites and follows a multi-stage process over many months⁴:

Stage 1: A mosquito ingests microscopic larvae when feeding on an infected animal.

Stage 2: The larvae develop within the mosquito over 10–14 days, especially in warm, humid conditions

Stage 3: The infected mosquito transmits the larvae to another pet during a subsequent bite

Stage 4: The larvae then migrate and mature in the heart and lungs over 6–8 months, causing progressive damage.

Unfortunately, heartworm infection do not often shows signs until it has progressed to advanced stages of disease. In dogs, symptoms may include persistent coughing, reduced exercise tolerance, weight loss and abdominal swelling. In cats, signs can include coughing, wheezing, or sudden collapse—often with little warning.
 

In addition, while heartworm disease in dogs can be treated with a complex combination of painful injections and medications, there is currently no approved treatment to eliminate heartworms in cats⁹. 
 

For these reasons, prevention remains the most effective way to protect your pet. To ensure your furry companion stays safe against heartworms all year-round, speak to your veterinarian about the NexGard® range, which offers broad protection in a simple, once-monthly solution:

NexGard SPECTRA®: A tasty, beef-flavoured chew that protects against heartworms, intestinal worms, fleas, ticks, and mites.

NexGard® COMBO: A topical solution that provides broad protection against heartworms, tapeworms, roundworms, hookworms, fleas, ticks, mange, and mites.

1. https://www.vetsforlife.com.sg/flea-and-worm-prevention-advice-from-a-vet-clinic-in-river-valley

2. https://www.webmd.com/pets/cats/what-to-know-heartworm-cats

3. https://www.webmd.com/pets/cats/what-to-know-heartworm-cat

4. https://www.heartwormsociety.org/heartworms-in-cats

5. https://www.heartwormsociety.org/pet-owner-resources/heartworm-basics

6. https://www.heartwormsociety.org/heartworms-in-dogs

7. https://www.heartwormsociety.org/heartworms-in-cats

8. https://www.fda.gov/animal-veterinary/animal-health-literacy/keep-worms-out-your-pets-heart-facts-about-heartworm-disease