5. Address the envelope. In the lower right third of the envelope, write the name of the person you are sending the letter to. Write the company name on the line below that (if there is a company name).
Once inside a new host, it takes approximately 6 months for the larvae to mature into adult heartworms. Once mature, heartworms can live for 5 to 7 years in dogs and up to 2 or 3 years in cats. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.
Heartworm disease in cats is a bit different than in dogs. Heartworms in cats do not live as long (average lifespan is only two to three years) or grow as long, and fewer of them mature into adults. Worm burdens are much lower in cats, with the average being only one to three worms.