Heartworm 101

Heartworm Disease Facts

  • Heartworm is a parasite transmitted by mosquitoes. Once an infected mosquito (one that has bitten a heartworm positive animal) has bitten a dog it takes 6 to 8 months for the larvae to develop into adult worms where they take up residence in the heart and lungs.
  • It is a slowly progressing disease.
  • Heartworm disease can cause blood clots, lung tissue scarring, pneumonia, an allergic lung condition and a heart murmur leading to heart failure and ultimately DEATH.
  • It has nothing to do with gastro-intestinal worms (round/whip/hook and tapeworm).


  • Not previously diagnosed in Queanbeyan dogs (those who have spent all their lives here) but cases have been diagnosed in dogs who have come from elsewhere and in Canberra.
  • Is prevalent in any coastal region especially north coast and up into Queensland. It is also prevalent in the high irrigation areas of NSW. Anywhere where mosquitoes are present.
  • Foxes can carry heartworm. As a result isolated, rural & farm dogs can also be at risk.

Clinical Signs

  • Mild cough
  • Increasing inactivity and lethargy. Exercise intolerance with increased coughing and breathlessness.
  • Fluid build-up in lungs and lower abdomen giving a swollen pear-shaped appearance.
  • Collapse (without warning) with deep laboured breathing, extreme weakness, blue tongue and pale gums.


  • The treatment of the disease can be fatal as dead adult worms can lodge in blood vessels.
  • Preventative medications work by eliminating the early life stage microfilaria before they mature into adult worms.
  • Although the risk is low for those owners who live in Queanbeyan and their dogs don’t go anywhere we still recommend all dogs are on some form of prevention due to the high mobility of people in this region and our close proximity to Sydney and coastal areas.

When to start a preventative medication

  • All dogs should start a preventative medication between 3 and 6 months of age and remain on a preventative medication for life.
  • Products available consist of daily tablets (not recommended), monthly tablets/chewables and top spots (sometimes combined with flea products) or yearly injection.
  • Missed medications or swapping between medications – please ask us how to do it safely.

WQVH recommendation: Our preference is for Proheart – SR12 yearly injection for its safety, convenience and decreased chance of missed medications. It can be done at the same time as your dogs’ annual health check and vaccination.


Testing for dogs over 6 months of age, not previously on heartworm prevention may be necessary – some preventative medications are dangerous given to dogs that are heartworm positive so please ask us.

Please ask one of our friendly team for advice on what product may best suit your pets needs.

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