Heartworm Disease in Dogs and Cats: What Pet Owners Need to Know

While April is Heartworm Awareness Month, pets in Malaysia are at risk all year round. The country’s hot, humid climate provides ideal conditions for mosquitoes - the carries of heartworm disease - to thrive. In fact, Malaysia is considered a high-risk  (hyperendemic) area for heartworm disease¹ particularly in urban centers².

Heartworm disease is a life-threatening condition caused by the parasitic roundworm - Dirofilaria immitis³. It is transmitted through the bite of an infected mosquito, which introduces microscopic larvae in the a pet’s bloodstream. 

Over time, these larvae migrate to the heart, lungs, and surrounding blood vessels, growing up to 30 cm in length, and cause serious damage⁴.

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

• In Dogs: Dogs are "definitive hosts”, meaning the heartworms can mature and reproduce within your pet. Without treatment, dogs can harbour hundreds of worms, potentially leading to impacted blood flow, organ damage and even heart failure. 

• In Cats: Cats are "atypical hosts" as heartworms do not survive to adulthood. However, even a small number can be dangerous as the immune response to the infection can cause Heartworm Associated Respiratory Disease (HARD), leading to inflammation and damage in the lungs that mimic asthma or bronchitis⁵.

Heartworm disease spreads only through mosquito bites and develops over several months⁶:

• Infection: A mosquito bites an infected animal (such as a stray dog or a wild animal) and ingests microscopic larvae (microfilariae).

• Incubation: The larvae develop inside the mosquito over 10 to 14 days, with development accelerated in warm, humid climates like Malaysia.

• Transmission: The infected mosquito bites a healthy pet, depositing larvae in the body via the bite wound.

• Maturation: The larvae migrates to the heart and lungs, maturing over 6 to 8 months and causing progressive damage.

Since heartworm disease develops gradually, early stages of infection don’t often show obvious symptoms. In fact, once symptoms appear, the condition might already be advanced. Nevertheless, typical signs that may indicate heartworm disease in dogs include⁷:

• Persistent cough

• Exercise intolerance or fatigue

• Weight loss or reduced appetite

• Laboured breathing

• Abdominal swelling

• Caval Syndrome: A sudden, life-threatening emergency marked by pale gums and dark urine.
 

In cats, signs are subtle and may mimic other respiratory conditions. Pet owners can stay vigilant by looking out for these signs⁸:
 

• Coughing or wheezing

• Intermittent vomiting

• Lethargy and weight loss

• Difficulty breathing

• Sudden collapse

While heartworm disease in dogs can be treated, the process is complex and involves multiple injections and medications to eliminate the worms and stabilise the animal. In addition, there is currently no approved treatment to eliminate heartworms in cats⁹. 
 

For this reason, prevention remains the most effective protection against this deadly disease. To ensure your pet stays protected year-round, speak to your veterinarian about the NexGard® range, which offers comprehensive parasite protection in a convenient once-monthly solution:
 

• NexGard SPECTRA®: A tasty, beef-flavoured chew that protects against heartworms, while also preventing intestinal worms and external parasites such as fleas, ticks and mites.

• NexGard® COMBO: A spot-on treatment designed to provide broad protection against heartworms, tapeworms, roundworms, hookworms, as well as fleas, ticks, mites and more.  

1.https://www.researchgate.net/publication/331056279_The_prevalence_and_trends_of_canine_heartworm_Dirofilaria_immitis_in_Kuala_Lumpur_Malaysia_1970-2018

2.https://www.researchgate.net/publication/331056279_The_prevalence_and_trends_of_canine_heartworm_Dirofilaria_immitis_in_Kuala_Lumpur_Malaysia_1970-2018

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

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

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

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

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

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

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