Ask the Vet

Tennessee, warmer climates have heartworm cases year-round

Q: We moved here from Michigan last year with our two dogs, Maddie and Millie. Our neighbors have been telling us all about heartworm disease and the need for pills every month. We didn’t do that in Michigan; we only gave the pills in the summer. Can you explain to me why it’s different here? R.T., Loudon

A: Welcome to East Tennessee. Transmission of heartworm disease depends on mosquitoes being present, and due to our warmer climate, mosquitoes can be present year round in Tennessee. The parasite is more prevalent in the Southern states with humid climates, where there is typically a higher mosquito population.

Heartworm disease has been documented in all 50 states, so it also is present in Michigan — but to a lesser extent.

As your vet in Michigan likely explained, heartworms are spread from mosquitoes infected with heartworms, which that mosquito, in turn, got from another dog or coyote.

If an infected mosquito bites your pet, it can inject microscopic heartworm larvae into Maddie or Millie. If your pets take their heartworms preventative pill that month, the larvae will die.

If Maddie and Millie are not taking their monthly medicine, the parasite will, instead, grow and mature inside them. The larvae will mature into adult heartworms, moving into the heart and surrounding arteries. There are male and female heartworms, and they reproduce to make the heartworm infection worse. Undetected and untreated, heartworm disease will lead to congestive heart failure and death.

It only takes one mosquito bite to transmit heartworms. Please talk to your veterinarian about heartworm prevention for Maddie and Millie.

Other options for heartworms include monthly topical medications or an injection that lasts for six months. Their blood should be tested for heartworms regularly.

Like so many diseases, prevention and/or early detection is important. For more information, is a great online source.

If you have questions about your pet, you may e-mail Myers at