Heartworm in dogs


Heartworm is a potentially fatal parasite (Dirofilaria immitis) that lives in the heart and the blood vessels around the heart.

What is heartworm disease?
Heartworm disease is a serious and potentially fatal disease in pets and is caused by foot-long worms that live in the heart, lungs and associated blood vessels of affected pets, causing severe lung disease, heart failure and damage to other organs in the body. Heartworm disease affects dogs, cats and ferrets, but the dog is a natural host, which means that heartworms that live inside the dog mature into adults, mate and produce offspring.

How is the disease transmitted?
The mosquito is an essential part of the heartworm life cycle. Adult female heartworms living in an infected dog, produce microscopic baby worms called microfilaria that circulate in the bloodstream. When a mosquito bites and takes a blood meal from an infected animal, it picks up these baby worms, which develop and mature into “infective stage” larvae over a period of 10 to 14 days. Then, when the infected mosquito bites another dog, cat, or susceptible wild animal, the infective larvae are deposited onto the surface of the animal’s skin and enter the new host through the mosquito’s bite wound. Once inside a new host, the larvae mature into adult heartworms in about six months.

How do we prevent heartworms?
Puppies should be started on injectable heartworm preventatives at 12-14 weeks of age. Some heartworm medications require two vaccinations in the first year of life, then every 12 months for life after that. You can usually synchronise the heartworm vaccination with your dog’s annual checkup and booster vaccinations. Other treatments require monthly topical application or feeding of a tablet.

Any dog over six months of age that hasn’t been on heartworm prevention will need a heartworm test prior to starting treatment. The test requires just a small blood sample from your pet, and it works by detecting the presence of heartworm proteins. If your pet tests positive, further tests may be ordered.

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