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Heartworm Disease And Prevention

Education > Dog Health & Behaviour 11th April 2019
 


Heartworm disease is a serious, progressive and potentially fatal disease caused by a parasite Dirofilaria immitis which is transmitted by mosquitoes. Heartworm disease occurs mostly in dogs and less commonly in cats. All dogs who are not on heartworm prevention are at risk of infection. Those living in landed properties or regularly walk in mosquito-prone areas are at higher risk.

HOW IS HEARTWORM DISEASE TRANSMITTED?

When a mosquito bites an infected animal, it picks up microscopic baby worms called microfilariae in the blood, which then develop into “infective stage” larvae. When this infected mosquito bites a dog, the larvae are deposited under the dog’s skin. It takes about 6 months for the larvae to mature into adult heartworms which lodge in the heart, lungs and surrounding blood vessels.



MOST DOGS CAN BE SUCCESSFULLY TREATED ESPECIALLY IN THE EARLY STAGES

The goal is to kill the microfilariae as well as adult worms through a series of injections while minimising the side effects of treatment. Dogs with advanced heartworm disease may require antibiotics, pain relief medications, diuretics to remove fluid accumulation and drugs to improve heart function.

  • Some dogs harbour several hundred worms which cause lasting damage to the heart, lungs and arteries.
  • In severe cases, the abdomen and legs swell from fluid accumulation.
  • The disease can lead to liver or kidney failure causing jaundice, anaemia and accumulation of toxins.
  • Severely affected dogs can develop a sudden blockage of blood flow within the heart leading to a life-threatening form of cardiovascular collapse called caval syndrome.



COMPLETE REST IS ESSENTIAL DURING TREATMENT

During treatment, it is very important to restrict exercise to decrease the chance of complications, especially pulmonary thromboembolism (clots in the vessels) as the worms die off. Signs of embolism include coughing, low grade fever and sudden breathing difficulty.

  • No running, playing, jumping.
  • Slow and short walks on leash.
  • Active, playful dogs need to be strictly confined to rest.
  • Some dogs need to be hospitalised for a few days.

A heartworm test will be done 6 months after treatment to confirm that all heartworms have been eliminated. Some dogs may require lifetime medication for heart failure.

HOW CAN WE PREVENT HEARTWORM DISEASE IN OUR DOGS?

Preventive Medication: Consult your vet on the appropriate heartworm preventives for your dog, e.g. pill, spot-on topical medication or injection to eliminate immature heartworm parasites.

Blood Tests: All dogs should be tested annually for heartworm infection as part of preventive care. If your dogs are older than 6 months and not on heartworm preventive, a simple blood test is done to ensure they are not already infected by the parasite before starting preventive medication.

Because no preventive medicine is 100% effective, annual testing is necessary to ensure the preventive medicine is working and to detect any infection in the early stage.

Mosquito Control: Remove any containers that may collect water. Clean out rain gutters regularly. Keep the grass short and rake up fallen leaves (which can hold water) to reduce breeding sites.