Heart Worm in Dogs

Heart worm is a parasitic disease, predominantly affecting dogs but also occurring in cats, it is caused by Dirofilaria immitis. Infective larvae or microfilariae develop in mosquitoes, and are transmitted to dogs when they are bitten. In dogs, they develop and migrate to the right side of the heart, where they mature. Adult worms attain lengths of 17–27 cm (7–11 inches), and they can survive for three to five years in the heart. As the number of heartworms in the dog's heart increases, the blood flow is compromised, and the animal shows signs of respiratory distress when it runs or exercises.

A dog may tolerate as many as 100 worms with minimal health problems unless it has excess stress. However whilst you cannot stop the dog bei8ng bitten in recent years drugs can stop the infected larvae developing in the dog. Treatment is more difficult as fragments of dead worms break off and can block the lung vessels and cause respiratory distress. Diagnosis is an X ray of the heart and lungs, an antigen test, and examination of a blood sample for microfilariae produced by adult females.

Cats can also be infected by Dirofilaria larvae. They do not tolerate a large worm load, and a single worm can be life-threatening.

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