July 29th
Heartworm and Prevention

What is heartworm?

Heartworm disease is a serious and potentially fatal disease. It is caused by foot-long worms, the tiny larva of which are transmitted between animals by mosquitos. Heartworm disease primarily affects domestic and wild canine species such as dogs, coyotes, foxes and wolves. Due to their proximity to urban areas, foxes and coyotes are considered important carriers of the disease. Heartworm disease can also be found in cats and ferrets but transmission in these species is much less common.

Adult worms can be found in the heart chambers and blood vessels of the lungs of affected dogs. Depending on the worm burden, this can lead to severe lung disease, heart failure and damage to other organs in the body due to reduced blood flow. In affected dogs, heartworm will mature into adults, mate and produce offspring. The cycle may be continued when a mosquito bites an infected dog and ingests minute heartworm larvae. After a brief pause to develop further in a mosquito, the larvae are ready to be transmitted into the next dog.

Once a dog becomes infected, treatment involves killing the adult worms living in the blood vessels of a dog’s heart and lungs. Aside from the high cost, treating a heartworm infected dog requires months of veterinary visits as well as strict exercise avoidance.

How do I prevent heartworm disease in my dog?

When it comes to heartworm disease, monthly preventive medication is infinitely preferable to the complicated, expensive and painful treatment for a dog who has become infected.

Heartworm prevention for dogs is easy, affordable and effective. Preventive medications are available as monthly tablets or topical medication and typically prevent parasites beyond heartworm. Your veterinarian will work with you to choose the most appropriate preventive medication for your dog and prescribe it for an appropriate amount of time. Decisions about the approach to prevention are based on the risk in the area, any expected travel plans and the duration of likely mosquito exposure. This is a discussion that needs to take place between pet owner and veterinarian in order to create an individual treatment plan for each dog.

Mosquito repellants and other products that claim to be natural preventive options are not recommended. Veterinarians will certainly recommend mosquito bite avoidance tools in any dog, but these cannot replace prescription preventive medication.

In Ontario, it is most common for six months of preventive medication to be prescribed, as mosquitos are active in warmer months. Heartworm medication works by eliminating immature stages of the heartworm parasite that may have been transmitted to a dog by a feeding mosquito. Since heartworms must be eliminated before they reach the adult stage, it is extremely important that heartworm preventives be administered strictly on schedule.

The American Heartworm Society recommends testing for all dogs. Testing provides surveillance data, typically tests for exposure to tick-borne disease at the same time and allows for early detection in rare cases of transmission.

Ask your veterinarian about heartworm testing and preventive medication to protect your dog against heartworm.