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.
Heartworms have to be present for 6 months before they are detectable by a heartworm test. While it is possible for a dog to get heartworm at less than 4 months of age it is not common. If this truly is heartworm then I would likely recommend the immiticide treatment which is unfortunately the expensive one.