Heartworm Guidelines

The Companion Animal Parasite Council (CAPC) has altered guidelines after evidence of preventive-resistant Diofilaria immitis strains was presented at the American Association of Veterinary Parasitologists Conference at the end of July in Chicago.

Researchers have now identified heartworm isolates from the Mississippi Delta region that develop in adult dogs receiving routine monthly heartworm preventives.

  1. This means treatment of heartworm positive dogs should be immediate and aggressive, as noted in the newly revised CAPC guidelines (for details, see capcvet.org).
  2. The “slow kill” therapy sometimes prescribed by veterinarians is no longer appropriate, as researchers have demonstrated that using this modality –repeated macrocyclic lactone administration over a period of time — increases the proportion of circulating microfilariae that possess resistance markers.
  3. Dogs should be tested for heartworms once a year. Existing infections should be aggressively treated with an approved adulticide and microfilariae should be eliminated.
  4. CAPC recommendations for year-round prevention with a broad-spectrum parasiticide should be followed.
  5. Pet owners should be encouraged to reduce exposure to mosquitoes as much as possible.

Specialists emphasize that evidence of resistance does not mean abandoning current protocols but that they be followed even more rigorously. The new evidence confirming heartworm resistance underscores the importance of protecting pets year-round without gaps in prevention.

Preventions are still the best protection we have and consistently administering them is key to maintaining pet health.