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Heartworms in Dogs: Facts and Myths

WebMD separates the facts from fiction about canine heartworms.
By Sandy Eckstein
WebMD Pet Health Feature
Reviewed by Amy Flowers, DVM

Heartworms in dogs are easy to prevent, but difficult and costly to cure. We asked Sheldon Rubin, 2007-2010 president of the American Heartworm Society, to separate facts from the myths about heartworm infestations in dogs.

 

Q: How do dogs get heartworms?

A: Only by the bite of an infected mosquito. There’s no other way dogs get heartworms. And there’s no way to tell if a mosquito is infected. That’s why prevention is so important.

Heartworm disease has been reported in all 50 states. And the bite of just one mosquito infected with the heartworm larvae will give your dog heartworm disease.

Heartworm disease has not only spread throughout the United States, but it’s also now found in areas where veterinarians used to say “Oh, we don’t have heartworm disease.” Areas like Oregon, California, Arizona, and desert areas -- where irrigation and building are allowing mosquitoes to survive. And if you have mosquitoes and you have animals, you’re going to have heartworms. It’s just that simple.

It takes about seven months, once a dog is bitten by an infected mosquito, for the larvae to mature into adult heartworms. They then lodge in the heart, lungs, and surrounding blood vessels and begin reproducing. Adult worms can grow up to 12 inches in length, can live 5-7 years, and a dog can have as many as 250 worms in its system.

 

Q: Can people get heartworms from their dogs?

A: It can only be passed on by mosquitoes. It’s a specific parasite that only affects dogs and cats and ferrets and other mammals. In rare cases, heartworms have infected people, but it does not complete its life cycle. The heartworm will migrate to the lung and cause a round lesion that looks like a tumor. But these are very rare cases.

 

Q: If one of my dogs has heartworms, can he give it to my other dogs?

A: No. Again, the only way heartworms are transmitted is through the bite of an infected mosquito. And even if an uninfected mosquito bit your infected dog, and then bit your uninfected dog the same night, he wouldn’t transmit the parasite from one dog to the other. That’s because when a mosquito bites an infected animal, the heartworm needs to undergo an incubation period in the mosquito before the mosquito can infect other animals.

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