The Tribune

By DR BASIL SANDS

Heartworm disease is becoming one of the more common ailments afflicting dogs today in the Bahamas. It is caused by the heartworm, Dirofilaria Immitis. This parasite lives in the right side (right ventricle) of the dog’s heart and the nearby large vessel (pulmonary arteries). As a result of them living in the heart, it damages the heart muscle and interferes with the normal function of the heart.

An intermediate host, the mosquito, is necessary to transmit the disease to dogs. The life cycle takes about six to seven months. The female worm produces large numbers of microscopic, immature heartworms that circulate in the blood. These immature worms are called microfilaria. They are taken up with the blood by a mosquito feeding on an infected dog.

In the Bahamas, because of our large stray dog population there is a large reservoir of infected dogs. After living in the mosquito for 10-14 days the microfilaria can then infect another dog that the mosquito feeds on. The feeding mosquito deposits infective microfilaria on the skin of another dog, and these enter the body through the mosquito’s bite wound. The microfilaria eventually travels to the heart where they develop into adult heartworms. The adult heartworms produce new microfilaria within three months. As mentioned earlier, it takes a least 6-7 months from the time the dog is bitten by an infected mosquito until the dog becomes a new source of infective microfilaria.

Heartworms are diagnosed by finding the microfilaria in the blood. Sometimes, however, no microfilaria is found in the blood and these cases are usually diagnosed by heartworm antigen tests. The reason why a dog can be infected without microfilaria being present in the blood is because the worms present in the heart are of the same sex and are unable to reproduce. Other times, the dog’s immune system clears away the microfilaria, but leaves the adult worms in the heart. Therefore, it is recommended that you have an antigen test done which is extremely accurate.

Common signs of heartworm disease are coughing, shortness of breath, and a reluctance to exercise. Some dogs may faint after exertion. Eventually the dog becomes weak, lifeless, loses weight and may cough up blood. Severe signs of late stage heartworm disease are congestive heart failure, abdominal swelling and laboured breathing. This condition may result in sudden collapse and death.

Once diagnosed, the dogs are evaluated for liver and kidney competency before being treated. Very rarely are the worms removed surgically. The newest and safest treatment is with a drug called immiticide. One injection is given in the epaxial muscle of the back daily for two treatments. This can be done in two days or two weeks based upon the health status of the dog and determined by your veterinarians. This drug eliminates virtually all side effects and is much more effective in producing a complete cure.

The treated dog can go home, but must undergo an enforced rest of several weeks until the dead worms are absorbed by the body. Unlike intestinal worms, when you treat a dog with these parasites, they pass out the worms directly in the faeces. However, because the heartworms are located in the heart, and once they are killed, they cannot be passed out. So they have to be absorbed by the body after they are dead.

By restricting the activity of the dog, this will prevent sudden movement of dead worm debris that might result from sudden exertion and that could cause life-threatening blockage or embolism when the dead worms can block a blood vessel. Embolism can cause lung damage and/or heart failure. In some sever cases, treating the dog with buffered aspirin after the treatment appears to reduce the risk.

In 4-6 weeks post treatment, the dog should be placed on a preventative medication. Several preventatives have been available for dogs for many years. These are normally given on a monthly basis. Personally, I like the Heartgard product. It is inexpensive and the dogs accept it very readily with very little side effects.

Preventing mosquito bites will eliminate the risk of disease however, this is nearly impossible. Preventative medications (Heargard) are a more effective option and are quite safe.