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Pet Talk: Preventing heartworms easier than treatment

Nadine Lober
Vail, CO Colorado

Along with melting snow and warmer weather, comes insects ” particularly mosquitos that can carry heartworm disease.

Heartworms are ugly worms (as most are), and they can cause a bad disease in pets. Heartworm disease is a parasitic disease that can affect any dog regardless of age, sex or habitat. There have been reported cases in cats as well.

It is spread by mosquitoes and is found, now, in virtually all parts of the United States. It is more prevalent along the Atlantic and Gulf coasts and Ohio and Mississippi river basins. There have been cases reported in the Denver region and other parts of Colorado, so preventative medication is important during the mosquito season ” or yearlong if your dog travels to infected warmer states.



The adult worm lives in a dog’s heart and adjacent vessels. It can grow up to four or 12 inches in length, reach maturation one year after infection and live for five to seven years. The adult heartworms living in the heart produce offspring, known as microfilaria, which circulate in the animal’s blood.

When a female mosquito bites an infected animal, it sucks out some blood containing these microfilaria. When this mosquito bites a pet, it will infect this pet with these larvae.

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Outdoor dogs are more likely to be infected than indoor dogs. Large dogs are more susceptible than small dogs, but length of coat does not appear to be a factor. Most dogs infected are between three and eight years old.

Once a dog has been infected with the larva from an infected mosquito, the larva migrates through body tissues for the next 100 days. At that time, young adult heartworms enter the blood system, travel to the arteries in the lungs and start damaging the lining of the vessels. The heart, lungs, and kidneys are all infected.

Symptomatic include coughing, fatigue, listlessness, weight loss, rough coat and aversion to exercise.

If your dog tests positive for the microfilaria or the adult worm, treatment must be initiated and is not simple. Most patients are hospitalized during treatment to kill the adult worm. The medication used is very strong and the effect of killing off the worms can potentially cause problems in the lungs. The circulating microfilaria are usually killed 4 to 6 weeks after getting rid of the adults.

The Vail Valley has only seen a few cases and usually in dogs who have traveled from other places. Preventing heartworm is easier than treating it. A blood test is always performed before starting an adult dog on the preventative medication, to insure no presence of larva in the blood.

There are many medications on the market now, such as: Heartguard, Interceptor and Revolution.


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