You may have heard of heartworm disease in dogs but, living in the north, you may not be especially concerned. However, like many parasites that have historically been more of a concern in the south, heartworm is also on the rise in Massachusetts. A decade ago veterinary clinics in eastern Mass generally saw about 1-5 new cases of heartworm disease in dogs each year, a concerning number for such a serious disease. Fast forward to today when most clinics are typically seeing 6-25 new cases of heartworm in dogs each year. Cats can catch heartworm, too, and statistics show that there is a similar increase in heartworm disease in cats in our area. This increase means that you probably have a pet that is infected with heartworms in your neighborhood.

Why the increase in heartworm? Heartworm disease is spread by the bite of a mosquito that has been feeding on an animal that is infected with heartworms. This feeding spreads baby heartworms from one animal to the other. Wild animals like foxes and coyotes are common sources, and had been typically the main source of infection for pets in this area. Parts of the country that tend to have year-round warm, humid weather that mosquitoes love tend to be hotbeds of heartworm disease. Disasters like hurricanes, overcrowded shelters, and animal rescue efforts have lead to a large population of dogs from these hotbed areas to be relocated to the north. Unfortunately, many of these dogs that get relocated to our area have not been on heartworm prevention and are already infected. Having so many dogs in the area that have heartworm increases the chance that each mosquito bite may carry baby heartworms.

Can’t I just treat my pet if they become infected? This is not the best strategy. Once a dog is infected with heartworms there can be long lasting damage to the heart and lungs even after the worms have been killed. Heartworm disease is an infection of parasitic worms that live in the large blood vessels of the heart and lungs and cause quite a bit of damage where they reside as you may imagine. The treatment itself is complicated, risky, very painful and quite expensive, often costing more than many years of prevention of the disease. There is no treatment currently available for cats and some cats can experience sudden death from heartworm disease.

What should I do for my dog? Puppies should be started on a monthly heartworm preventative at the time of their first vaccines and should continue to take a preventative every month for the rest of their lives. Yearly testing is recommended to ensure that they remain negative. The preventatives that exist these days are pretty good at preventing disease but there is nothing that exists that is a 100% guarantee against infection. If a dose of preventative gets missed then the dog is at risk if they are bitten by an infected mosquito. Yearly testing ensures that infected dogs do not go very long without being detected. Treatment of heartworm disease is easier on the dog if the infection is not too far advanced.

What about my cat? Although cats do not catch heartworm as easily as dogs, every cat that has a chance of exposure to mosquitoes (basically all cats) should be on a preventative every month from the time they are a kitten.

Prevention is much easier now than in the past. A couple of decades ago dogs had to be given daily preventatives that could become dangerous if a single dose was missed. These days there are many monthly options from yummy treats to topicals. Most heartworm preventatives are combined with other helpful preventatives so it is possible to prevent intestinal parasites or fleas along with a range of other parasites in the same monthly dose. Your veterinarian can help you pick the best option for your pet’s lifestyle and your preference.

If you would like to read more about heartworm disease the American Heartworm Society has great resources for pet owners.