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Heartworm Disease


Heartworm disease in dogs

Found in numerous locations across Australia, heartworm is an often-deadly parasitic disease for dogs spread by mosquitos. Larvae are picked up by mosquitos after biting an infected dog, before being transmitted to a healthy dog by a mosquito bite. After six months, the larvae grow into adult worms that live in the heart and vessels around the lungs. Left untreated, heartworms can reproduce and grow, causing blockages of major vessels and serious disease. Fortunately, there are effective means for preventing this disease.

Prevention of heartworm disease

There are many effective heartworm prevention options on the market. If heartworm is an endemic in your area, your vet will be able to tell you help you with the best preventative plan for your pet. Many pet owners manage the risk of heartworm disease with the yearly injection, as this removes the risk of forgetting a dose of preventative medication and your vet can administer this injection as part of your pet’s regular health check.

The other option is to make sure your dog is on heartworm prevention medication year-round. There are two main types of preventatives; monthly preventatives that come in a spot on or tablet form (often combined with other types of worming and flea medications) and a yearly injection, however even one missed dose can put them at risk of heartworm disease if you choose this method.

Symptoms of heartworm disease

When dogs are infected with larvae, they don’t usually show any clinical signs of the disease. However, once adult worms have grown and reproduced, disease associated with blockage is often seen.

Symptoms of clinical heartworm disease include:

  • Low exercise threshold (exercise intolerance)
  • Lethargy and weakness
  • A dry and persistent cough
  • Weight loss

In more severe cases, when the heart and lungs have been extensively damaged by the worm burden, symptoms include:

  • Rapid and shallow breathing
  • Swollen abdomen
  • Sudden collapse
  • Blueish tinge to gums
  • Sudden death (particularly after exercise)

Diagnosis and treatment of heartworm disease

Diagnosing heartworm involves a couple of steps. After six months, adult heartworms can be detected from a rapid bedside test using a drop of blood. Your veterinarian will then look at your dog’s blood under the microscope to look for worm larvae. They might also send a sample off to a diagnostic lab.

Once the blood test confirms the disease, your vet can stage the infection by taking chest X-rays and taking further blood tests to check the degree of damage caused by the infection. Treatment can be risky and prolonged, so prevention is definitely the best cure when it comes to heartworm disease.

Heartworm disease in cats

Heartworm can infect cats as well as dogs, however the disease is very different in cats. Most cats that are bitten by infected mosquitos only have a short, limited infection, as their immune system kills the larvae before they can grow into adult worms.

This also means that heartworm disease is more difficult to diagnose in cats. Although the infection is usually self-limiting in cats, it can cause an allergic reaction and immune response that damages their lungs.

Symptoms of feline heartworm can often mimic feline asthma, another respiratory condition of cats. If you’re in an endemic heartworm region and your cat is showing signs of feline asthma, your vet should consider testing for heartworm, even though it’s a rare condition in cats.

Fortunately, there are monthly spot-on treatments for cats which protect them against heartworm disease, and as with dogs, prevention is always better than cure.