Heartworm Disease

What is Heartworm Disease?

  • A parasite transmitted by mosquitos to your pet (dogs and cats specifically) that resides in the major blood vessels of the heart and lungs.
  • A single bite from a mosquito can infect your pet.

Where is Heartworm Disease Found?

  • Everywhere
  • The incidence maps below show the number of cases reported in the US over the past few years.  Keep in mind that some clinics do not test properly or do not report positive results to the American Heartworm Association.  As seen below, the incidence especially in the Midwest has grown considerably over the past 3 years.  2014 and 2015 have not been formulated.

How to Prevent Heartworm Disease?

  • Mosquitoes are present all year contrary to popular belief.  They can overwinter in microclimates such as a garage, greenhouse or any place where a warm environment can be maintained. 
  • For this reason, prevention should be given year round. 
  • Prevention is available for both cats and dogs in a variety of forms.  Regardless of product, annual heartworm testing is required to initially receive heartworm prevention and to continue to be on this prescription.  This is to prevent and detect resistance to any medication before it becomes a catastrophic issue.  It also protects your pet from any negative effects of receiving medications when infected.
  • Most approved products are given every 30 days (once a month).

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How do you Test for Heartworm?

  • Tests commonly used for heartworm disease are those that test for antigens.  
    • Puppies are not required to be tested until 7 months of age due to the life cycle of the worm.
  • They are not foolproof however, as the antigen is only produced by adult female worms
    • Therefore if any entirely male infection or young infection exists, the test will not detect that process.
  • Some veterinarians implement a microfilarial test which when done appropriately can be very effective.  Unfortunately, many do not use the correct process and slides to make this an accurate diagnosis.  A single drop of blood on a slide is NOT diagnostic and will lead to false security.  
  • Cats are difficult to test accurately as there are less likely to be adult worms present.  Therefore both an antigen (part of the worm) as well as an antibody (cat's immune response to worm) testing is needed.

How is Heartworm Disease Treated?

  • Heartworm disease treatment is hard on the pet and the pocketbook.  There is also no treatment available for cats.
  • After a positive test is made, a blood sample is collected and submitted to a lab for confirmation.
  • If confirmation of infection is made, radiographs are taken of the heart and chest to allow your veterinarian to grade the severity of disease and therefore appropriately plan treatment.
  • There is only one approved technique to treat heartworm infection and it is not a cure.
    • This technique involves injection of an arsenic-based compound.
    • It requires weeks if not months of complete activity restriction.
    • Antibiotics are also used in conjunction with this treatment and continuation of prevention is necessary to control further infections.                       

How is My Cat Different than My Dog Concerning Heartworm Disease?

  • We do not generally associate cats with heartworm disease.   In fact, their population is relatively underrepresented in ads concerning this problem.
  • The fact is that cats also get heartworm disease but there is no treatment available. 
  • Cats also have a profound inflammatory and immune reaction to presence of heartworm larvae.
    • Many are killed by the cat before they can become an issue.
    • Large worms can cause more severe issues due to the profound immune response and damage to the vessels of the heart and lung.
  • Many cats with heartworm disease are misdiagnosed as having asthma or an allergic reaction.
  • On average, an adult worm can live 5 years in a dog and only 2-3 years in a cat.
    • Many protocols used as treatments involve waiting for these worms to die naturally and using oral preventative to avoid reinfection.

Sources for Additional Information:


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