Heartworm Disease and Prevention

Life cycle and transmission

Heartworm is a worm that lives in the heart of dogs and occasionally cats. An infected animal carries baby heartworms (called microfilariae) in the blood. When a mosquito bites an infected animal, it can then later bite an uninfected animal and introduce the microfilariae into the blood of the uninfected animal. Over a period of 4-6 months, the microfilariae gradually grow into adult heartworms which live within the heart and/or the main blood vessels going in and out of the heart.


Signs of Heartworm Disease

Heartworm can cause severe obstruction to normal blood flow around the body. Infected animals may not show any signs of illness in the first several years, but are still capable of spreading the disease to other dogs via mosquito bites during this period. When the infection has progressed more severely, signs noticed include inability to exercise for normal periods of time (exercise intolerance), tiredness, coughing and/or breathing difficulties. The worms can also cause blood clots within the blood stream, which can block blood flow to major organs such as the brain or lungs and cause immediate death.


Diagnosis and Treatment of Heartworm Disease

If signs are noted in your dog (or cat), and your pet is not on up-to-date heartworm prevention, please consult your veterinarian immediately. As these signs could indicate other diseases as well, a heartworm blood test might be recommended in conjunction with other tests to arrive at an accurate diagnosis.

Heartworm can be treated in dogs with a course of injections over a 1-2 month period. However, treatment comes with complications and side effects, some of which may be serious, and your pet needs to be strictly confined to rest during the period of treatment to minimise these complications. Prevention is indeed always better than cure.

Even though the heartworm in dogs and cats is of the same species, there is no reliable and safe method of diagnosing and treating heartworm disease in cats. However, the likelihood of infection in cats is thought to be much lower than in dogs as the heartworms prefer dogs as their host.


Heartworm Prevention

As heartworm disease exists in Singapore and can be a life-threatening infectious disease that remains silent for a long period of time, prevention is highly recommended, especially in dogs. If your dog is more than 6 months old, it will require a simple and quick blood test to ensure that it is free of heartworm. You can then start on heartworm prevention, which may be given as monthly oral tablets or spot-ons (applied onto the skin) or yearly injections. It is essential that doses of heartworm prevention are not missed thereafter, otherwise there might be a chance of infection. Please call your veterinarian for advice should you miss dose(s) of heartworm prevention.

Heartworm prevention should never be started without your veterinarian's advice and prescription for the safety of your pet.