Canine Heartworm Disease

Heartworm disease is a very serious illness that can be fatal to dogs. As the name suggests, the condition involves worms (Dirofilaria immitis) that reside in the heart and major blood vessels of the body.

The disease is transmitted to dogs by mosquito bites. The heartworms enter the dog as larvae in the saliva of the female mosquitoes. (It is always the female mosquito that delivers a bite; male mosquitoes do not feed on blood.) Before a mosquito takes a blood meal, she first pumps a small amount of saliva into the wound and this serves as an anticoagulant to allow her to draw blood more freely. Along with the saliva, she may also inject a variety of diseases. In the case of heartworm disease, a simple mosquito bite can initiate a devastating disease process that takes years to develop. The heartworm larvae may enter the skin through the insect bite and burrow further where it can stay for 3-4 months. If this occurs in a human, the worms usually die; our species is not considered a suitable host. In dogs, however, the worms may find their way to the heart and grow. Only then will outward symptoms develop in the dog.

Heartworm symptoms in dogs may develop very slowly. In fact, most symptoms are not detected until several months (or even years) after the initial infection occurs. For this reason, the disease is very rarely diagnosed in puppies. The symptoms can include chronic coughing, fatigue, and labored breathing. The heartworms clog the heart and major blood vessels that lead from the heart, causing the blood supply to other organs of the body to be reduced. Many dogs develop lung, heart, or circulatory problems as the disease progresses. If these symptoms are left untreated, most dogs will collapse during the final stage of the disease.

As with many treatments, there are risks involved in treating heartworms. This is because the treatment of choice contains arsenic, a well-known poison. The key goal in treatment, of course, is to kill the heartworms without harming the dog. Fortunately, more than 95% of all treated cases are successful. The typical heartworm treatment is a 2-day course that kills the adult heartworms over a period of 30 days. After one month, a follow-up clinic visit provides an additional drug to kill the microfilariae. A repeat course may be advised. Recommendations may also include a special diet, antibiotics, or diuretics to remove any fluids that have accumulated in the dog's body. Heartworm disease can be effectively controlled and prevented with specific medication. Annual trips to the veterinarian are advised for preventing this deadly disease.

If a dog spends most of its time outdoors, a topical mosquito repellant also may be recommended for extra protection. However, NEVER use DEET-based products directly on a dog; he will tend to lick it off and risk being poisoned. There are several "pet-friendly" mosquito repellant products that are more suitable for use. Additional anti-mosquito measures can be implemented, including standard precautions such as removal of standing water from the yard, application of pet-safe larvacide to unmovable water, and staying indoors during peak time of mosquito activity. As with all pet ailments, if a dog exhibits any of the symptoms of heartworm disease, seek medical attention immediately.