Heartworm Infections

Heartworms are observed in many areas of the country and are transmitted by the bite of a mosquito that has previously bitten an infected dog or cat. For reasons that are not clear, the percentage of infective larvae developing into worms is significantly less in cats than in dogs.

The heartworm cycle begins as larvae work their way into the cat’s heart where they develop into adult heartworms. The mature worms settle in the right side of the heart and in the lungs. This causes the heart to work harder to pump blood to the lungs. As the heart weakens, the insufficient blood flow affects every other organ in the body.

Heartworm disease in cats may be acute or chronic. In acute cases, infected cats may have no signs of illness and may die suddenly. Only a postmortem examination by a veterinarian can identify heartworm infection as the cause of death. Sudden death is often attributed to circulatory collapse and respiratory failure.

Signs of chronic infection include coughing, weight loss, lethargy and vomiting. Infected cats can be treated, but the treatment is a serious undertaking requiring hospitalization and may or may not be successful.

Cats housed indoors are the least likely to become infected. Cats at the greatest risk of heartworm are those in an area where mosquito infestation is heavy. Male cats are more susceptible to heartworm infection than females, in terms of the number infected and the number of heartworms present per cat. This higher percentage for males may be the result of their roaming outdoors more than females or perhaps because males produce more suitable conditions of the development of heartworm larvae.

Veterinarians may suggest heartworm medication for cats in high risk areas.