Plymouth County Mosquito Control Project

Dog Heartworm

     Dog heartworm can be a life-threatening disease for canines. The disease is caused by the roundworm Dirofilaria immitis. Dogs and sometimes other animals such as cats, foxes and raccoons are infected with the worm through the bite of a mosquito carrying the larvae of the worm. While cats are susceptible to the disease they do not appear to be good hosts. As a result cat infections are rare. Dirofilaria immitis is found throughout much of the United States including Massachusetts. Many common mosquito species in Massachusetts can become infected with the worm.

     Dirofilaria immitis is dependent on both the canine and the mosquito to fulfill its lifecycle. In an infected dog the adult worms are 9-16 inches in length and live in the dog's heart and lungs. The young worms called microfilaria circulate in the blood stream of the dog. These worms must infect a mosquito in order to complete their lifecycle. Mosquitoes become infected when they blood feed on the sick dog. Once inside the mosquito the microfilaria leave the gut of the mosquito and live in the body of the insect, where they develop for 2-3 weeks. After transforming twice in one mosquito the third stage infective larvae move to the mosquito's mouthparts, where they will be able to infect an animal. When the mosquito blood feeds, the infective larvae are deposited on the surface of the skin. The larvae enter the skin through the wound caused by the mosquito bite. The worms burrow into the skin where they remain for 3-4 months. If the worms have infected an unsuitable host such as a human the worms usually die at this point. If the infective larvae are in a suitable host they will eventually enter the blood stream and locate the heart of the animal. Once they are in the heart they will reach the adult stage after about 5 months. In all the lifecycle of Dirofilaria immitis takes about 9 months to complete.

 Dog heartworm

Dog Heartworm Life Cycle


     While dog to dog transmission is not possible, the presence of an infected dog or other animal in the neighborhood can serve as a reservoir for the disease. The outbreak is caused when mosquitoes ingest microfilaria and in turn infect other animals.

     Symptoms are not usually apparent until the adult worms have damaged the heart and other organs as a result of reduced blood flow. Some of the symptoms include, weight loss, shortness of breath, weakness, chronic cough, chronic heart failure and death. Because symptoms take so long to appear it is important to get your pet tested regularly for dog heartworm. Dog heartworm can be detected through a blood test that looks for the microfilaria circulating in the blood. It can also be detected through an X-ray.

     The cure of dog heartworm can be an expensive and sometimes risky. The veterinarian must administer toxic chemicals to kill the worms over a period of time. If all the worms were killed at once the worms would move into the lungs and asphyxiate the dog. Surgery is sometimes possible as well.

     The best way to deal with dog heartworm is to prevent the dog from becoming infected. There are several pills that can be given on a monthly or daily basis. The chemical in the pill kills any infective stage larvae circulating in the dogs' blood, thus preventing an infection. Since infected canines can have a reaction to the medication, the dog should be tested for dog heartworm before administering any of these pills. A veterinarian should conduct the tests.

     Please remember that prevention of dog heartworm is part of being a responsible dog owner.

Links to more information:


American Heartworm Society

American Veterinary Medical Association

Does your dog have heartworm? - New Jersey Mosquito Control

 

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