“How Can You Mend a Broken Heart?”

Bee Gees

April is Heartworm Awareness Month.  Heartworm disease is a serious and potentially fatal condition where adult heartworms live in the heart and adjacent large blood vessels of infected dogs. The female worm is 6 – 14″ long and 1/8″ wide, and the male is about half that size. One dog’s system may contain as many as 300 worms.  Adult heartworms may live up to five years with the female producing millions of offspring called microfilaria that live mainly in small vessels of the bloodstream.

The only way heartworms are transmitted is through the bite of an infected mosquito, but since transmission requires the mosquito as an intermediate host for the microfilaria to mature, the disease is not spread directly from dog to dog.  The bite of just one mosquito infected with the heartworm larvae will cause heartworm disease.  Spread of the disease coincides with mosquito season, which can last year-round in many parts of the United States.

When I was in practice on Cape Cod, we began seeing a few cases of Heartworm disease in the early 70’s, and now it has been reported in all 50 states. The highest numbers of reported cases are still within 150 miles of the Gulf of Mexico, the Atlantic Ocean coastlines and along the Mississippi River and its tributaries. According to an American Heartworm Society survey, the number of cases of heartworm disease seen per veterinary clinic was 22 percent higher in 2016 than in 2013, and the AHS is predicting more heartworm disease this year.

Heartworm disease can be prevented with prescription medications available in pill, topical or injectable forms, but your pet needs to be tested prior to beginning any preventive medication to make sure that infection hasn’t already occurred. This is critical because animals may not show signs of the condition for the first six months or more following infection, but can react badly – even fatally – if preventive medication is given to a dog already infected.

There are various ways to detect the disease.  The serological test (antigen test, ELISA or SNAP test) is the most widely used test to detect antigens produced by adult heartworms.  With the Knott’s test, a blood sample is examined under the microscope for the presence of microfilariae.  However, approximately 20% of dogs do not test positive, even though they have heartworms because their immune system has acquired the ability to destroy the microfilariae.  Thus the antigen test is preferred for diagnosis.

Heartworm disease can be treated, although the disease may go unrecognized by pet owners because initially there are no clinical signs. But as more and more worms crowd the heart and lungs, dogs will develop a cough and gradually be unable to exercise and start retaining fluids. Eventually, dogs will die if the worms are not eliminated.  An injectable drug to kill adult heartworms occupying the heart and adjacent vessels is administered by your veterinarian.  Antibiotics, steroids and function-specific animal supplements are usually given also.  Following treatment, your dog will be started on a heartworm preventative and maintained on animal supplements.

Although somewhat risky, expensive and worrisome to pet owners, 95% of infected dogs can be successfully treated. Prevention is key, but if your dog does become infected, veterinarians have all the tools to help mend a broken heart.

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