In the past few years a number of dogs have been found to have heartworm, a parasite transmitted by a mosquito bite.

What causes heartworms in dogs?

Heartworms are fairly long (20 to 30 centimeters) and slender, and live in the major blood vessels and in the right-side chambers of the heart.

The presence of heartworms over a long period brings about a thickening of these important blood vessels which affects the circulation to the heart muscle.

Sometimes the parasite dies creating a blockage within the blood vessel and producing severe and rapidly developing symptoms of heart. Large masses of worms may impair the circulation from the liver and lungs and may interfere with the proper functioning of the kidneys.

Symptoms of heartworms in dogs

  1. The affected dog becomes less able to exercise, may have a chronic cough and develops symptoms associated with a failing heart.
  2. Affected dogs appear to age prematurely, may become grey around the muzzle and have a much reduced life expectancy.

Treatment for heartworms in dogs

Most veterinarian surgeons are advising their clients to use a preventive daily, dose of Diethylcarbamazine (DEC) tablets. Puppies can be started on these tablets at three months.

Other dogs must be first tested by a vet because it can be dangerous to start preventive treatment on an adult dog without ensuring it is free of the disease. Infected dogs may become shocked and die from quite low doses of DEC.

Treating heartworm consists of the administration of an organic arsenical compound over 48 hours. If the dog has not suffered irreparable damage to heart vessels and liver, treatment is usually quite successful.

There is a risk that dead parasites may block large blood vessels so it is important that dogs are kept very quiet for some weeks after treatment. After removal of the adult worms, the immature stages circulating in the blood are treated with another chemical.

If continuous medication is rejected, it is most important that dogs are tested annually, say at the time of vaccination. If this is done, and if the disease is subsequently discovered, it will be at a stage where treatment should be effective and would reduce the risk of side effects.

If the animal is taken into the higher risk areas, preventive treatment should be given, not only during the course of the stay but for three months afterward. This preventive treatment must only begin after a recent blood test has proved negative. The risk of infection can be reduced if the dog’s sleeping areas are screened against mosquitoes.

Discuss the problem with your veterinarian surgeon to make sure that you are aware of any advances in treatment or prevention.