Heartworm infection has been found in dogs in all 50 states, but is highly preventable with monthly medications that kill heartworm larvae before they become adults. Most veterinarians and organizations recommend year-round heartworm prevention, in part to increase owner compliance, especially during peak transmission times.

On the Other: Seasonal Prevention (Six Pills)

Heartworm larvae cannot be transmitted until specific temperature conditions are met. For most of the United States and Canada, these conditions occur fewer than six months out of the year. The southeastern United States meets the conditions most of the year. A conservative seasonal guideline is to give heartworm medication from June through November to dogs living above the North Carolina-Virginia state line.

Bottom Line

Not all dogs need year-round heartworm medication, but some owners might have trouble with a seasonal pill schedule. Veterinarians and owners should discuss heartworm prevention, taking into consideration the regional climate and the likelihood of owner compliance, and decide on a program that provides maximum protection with minimal risk of side effects. Annual heartworm testing is recommended regardless of location.

Source:

American Heartworm Society: Canine Guidelines

American Heartworm Society: Frequently Asked Questions

More Information:

Companion Animal Parasite Council: Heartworm Recommendations