Treatment of Canine Heartworms

Most people give their dogs heartworm medicine to prevent the development of heartworms.  However, occasionally heartworms do infect a dog.  What happens then?  Heartworm treatment is a serious thing, but gone are the days when arsenic was administered to the dog in an effort to kill the heartworms but not the dog.

A dog gets heartworms when he is bitten by an infected mosquito.  The mosquito transmits the heartworm larvae into the bloodstream.  The larvae grows and migrates to the heart and lungs and associated arteries.  It mates and releases microfilariae, which will grow up to be heartworms if not killed. Heartworms irritate the lining of the arteries between the lungs and heart.  They reside in the lungs and heart.  The heart must pump harder to get blood through the irritated arteries and the heartworm clogged lungs and heart.  This leads to congestive heart failure and death.  Heartworms also damage the liver by causing fluid to back up in the body as the heart fails.  Dog age prematurely and gray about the muzzle and feet.  They loose the bounce in their step and act old as well.  Active dogs are more effected than couch potatoes as they put more demands on their heart and lungs.

If detected in time, however, heartworms can be treated. The dog is given an adulticide to kill the adults and a microfilaricide to kill the microfilariae.  This must be accomplished with a minimum of complications from the dying worms and the administration of the drugs.

There is currently only one drug approved by the FDA to treat adult heartworms in dogs.  It is an organic arsenic compound that is gentler than the drugs used in the past.  Melarsomine dihydrochloride is administered in a shot to the lumbar region of the dog.  The primary complication for the dog from the adulticide is the development of pulmonary thromboembolism.  This is a clogging of the pulmonary arteries by the dead heartworms.  If the adulticide is successful, dogs always have some degree of pulmonary thromboembolism.  Dogs with severe infections often require administration of corticosteroids to reduce inflammation from the dead heartworms.

The presence of the dead heartworms in the pulmonary arteries are why it is very important to confine dogs treated for heartworms for six to eight weeks to keep them quiet while their body eliminates the dead heartworms.  Exercise will result in lesions in the pulmonary arteries and death.

To treat the microfilariae, dogs are administered a commercial heartworm preventative.  This is an off label usage of the drug, but there is currently no approved microlifaricide.  Dogs should be observed for at least eight hours after treatment with a microlifaricide to ensure there are no complications from the dead microfilariae.

Today most veterinarians treat microfilariae infections by administering preventatives as usual and slowly clearing the microfilariae over a period of six to nine months without danger to the dog.

As you can see, treating heartworms is a severe shock to the dog’s system.  It is much cheaper and more humane to administer one of the many heartworm preventatives available to dogs than to allow them to come down with heartworms.