News & Articles

‘Tis Always the Season: Why You Should Use Heartworm Prevention

Posted on: April 10th, 2015

by Dr. Sharon Davis

Any pet owner who has grown up in New England has heard the term “Heartworm Season”. Many think that heartworm season is limited to the summer months when the weather is warm. Times have changed; if there was ever a true heartworm season, it exists no more. Heartworms are transmitted year round, even in New England.
There are several reasons heartworm prevention should be given year round.

• Mosquitos have evolved. They are adapting to living in colder climates, living longer, traveling further, and more mosquitos are carrying infective heartworm larvae than ever before. From year to year, no one can predict the first day warm enough day for mosquitos to bite or when the mosquito activity will end in the fall. Environmental changes, both natural climate changes and manmade changes such as real estate development or change in water drainage, have led to longer mosquito seasons. Did you know that adult mosquitos can hibernate for as long as 5 months in winter weather? It is not unusual to see a sleepy mosquito indoors during the winter, often brought in on a piece of wood for the fireplace. In addition to being able to feed indoors in winter, these hibernators become active and start feeding outdoors earlier in the spring season than ever before. And they can travel up to two miles for a blood meal!

• People and pets are traveling further and more often. Heartworm disease can now be found in all 50 states. Pet owners may unknowingly travel to areas with higher incidences of heartworm disease, infecting their own dog, and then carrying it back home. Stray dogs, many already infected, are now routinely transported all over the country to be adopted into new homes. There has been a significant increase in heartworm cases each year especially since Hurricane Katrina in 2005, after which at least 80,000 of the misplaced dogs were transported to New England. Heartworm cases in New England jumped from approximately 1750 in 2011 to around 3500 in just the last 3 years. Did you know that there have been over 60 confirmed Heartworm cases in New Hampshire so far this year?

• Dogs are not the only carriers of heartworm. Infective heartworm larvae are carried in several wildlife species, such as coyotes, fox and wolves. Enough of our local wildlife are carriers at this point that we will never eradicate heartworm disease. Often not talked about, pet cats and ferrets can also be infected and die from heartworm disease.

• In addition to preventing heartworm infection, monthly heartworm preventatives prevent the most common intestinal parasites. These include roundworms, hookworms, and whipworms, all of which are ubiquitous in our environment. These parasites not only cause disease in dogs but pose serious health risks to people.

• Finally, it is far easier, safer, and less expensive to prevent heartworm disease than to treat an infection. Before a dog infected with heartworms starts to show obvious signs of illness, the infection can be silent. There is a treatment for dogs, but it can take a long time and be very expensive. Furthermore, although the worms can be eliminated, we cannot always repair the damage that has already been done to the heart and other organs during infection. Be aware also, there is no safe treatment for cats or ferrets.

Plan to have your dog tested at least once annually for heartworm exposure, and keep them protected from heartworm disease by giving a monthly oral preventative. We recommend Sentinel for monthly heartworm and parasite prevention. Sentinel is given orally to your pet on a monthly basis. Currently, there is a $10 mail in rebate when you purchase a 6 month package.

For more information, please call us at (603) 335-2120. You can also find in depth and accurate information from the American Heartworm Society at and the Companion Animal Parasite Council at

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