Are Heartworms Contagious

Heartworm disease is not contagious, so it can not be passed directly from one animal to another. Instead, it is spread by mosquitoes. When a mosquito bites a dog that is infected with heartworm disease, it becomes infected with microfilariae, better known as heartworm larvae. The larvae mature within the mosquito and are transmitted to another animal when the mosquito bites them.

Heartworms are most common in dogs, but they can also be found in cats, ferrets, foxes, wolves and very rarely even in people.

The heartworm life cycle:

Once an animal has been bitten by an infected mosquito, it takes two to three months before the larvae develop into adult worms in the heart and pulmonary vessels. It then takes another three to four months before the heartworms fully mature and start producing offspring.

This means that it takes six to seven months after a dog has been bitten by an infected mosquito before heartworm disease can be diagnosed. Adult heartworms can live for five to seven years in a dog and an infected dog can have between one and 250 worms living in their heart and pulmonary vessels.


Since heartworm disease is transmitted by mosquitoes, it is much more common in warm climates with a lot of stagnant water like here in Florida. Heartworm disease is very serious and potentially fatal. It is expensive to treat but is very easy and inexpensive to prevent.

With the warm climate in Florida, it is important that your dog is on monthly heartworm prevention year round. In fact, the American Heartworm Society recommends giving heartworm prevention to your pet every month regardless of the area that you live in.

A lot of pet owners mistakenly think that their indoor pet does not need to receive heartworm prevention. Because mosquitoes can easily come indoors through open windows or doors, it is vital to ensure that indoor dogs are given heartworm prevention. Additionally, most indoor dogs are walked outside to use the bathroom.

Heartworm prevention is a prescription product so it can only be obtained through a veterinarian. There are several different types of heartworm prevention available and the prevention only needs to be given monthly. Your dog or cat will require at least an annual exam and heartworm test to stay current on their heartworm prevention, but you should discuss recommendations with your veterinarian.

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