Dear Dr. John,

I have read your column with interest for a long time! It has always been a great source of information. Today I write to you regarding heartworm and how often preventatives should be given. Some of my friends have been told that since we are in the Northeast that there is much less risk for heartworm disease to occur and, as such, the preventative monthly pills need only be given during the warmer summer months. Is that correct or appropriate? I have always given my dogs the heartworm preventative medications throughout the year as my vet has always suggested. D.C.

Dear D.C.,

Thank you for your kind words. I have been writing my column going back to 1987 and it has been gratifying to think that I have been able to answer questions and give advice about pets and matters relating to veterinary medicine for so long.

Your question is timely as we step into the warmer summer months and, interestingly enough, my first column was about heartworm! To my chagrin, there are a few veterinarians in the northern states that do not emphasize the need for heartworm preventatives to be given year-round. Since heartworm is transmitted by mosquitoes, those doctors and some owners do not see the need for such protection. That is a wrongful assumption and a recent report based on 2022 and 2023 data has shown an increase in incidence of heartworm, not only in known prevalent areas such as the Deep South but also unexpected states such as Connecticut and Massachusetts.

This is primarily due to insufficient use of preventatives, warmer temperatures allowing mosquitoes to exist around here even in winter months with warm spells, and mostly from adoption of dogs from areas where there is more heartworm disease.

In summary, I do not feel it sufficient or appropriate to give heartworm preventative less than year-round and many of those products give added benefit of protecting against intestinal parasites as well, so keep giving your dog’s preventatives as you always have and hope your friends do the same.

Dr. John de Jong owns and operates the Boston Mobile Veterinary Clinic. He can be reached at 781-899-9994.