Dear Spring Oaks’ Family:

The April topic of the month is heartworm prevention in dogs and cats.

Heartworms are very common in Florida due to our warm climate and large numbers of mosquitoes.   While heartworms can kill dogs and cats, fortunately they are completely preventable.

Heartworms are named “heartworms” because the adult worms in dogs live in the arteries that go from the heart to the lungs.  Sometimes there are so many worms that they can be found in the right side of the heart itself.  These worms feed on blood, and their bodies impede blood flow.  They may cause the dog to cough, have exercise intolerance, and even have congestive heart failure.  Once a dog is in congestive heart failure, he or she may lose weight, have fluid in the belly, have difficulty breathing and die. 

Cats can also get heartworms but they tend to cause problems in the lungs rather than the heart.  Cats may also cough, have difficulty breathing, or vomit with heartworms but they may also show no signs at all and suddenly die when stressed.

When we test a dog for heartworms, we are looking for a protein that is produced by the adult female heartworms.  Since heartworms take six months to mature and start producing this protein we do not routinely test young puppies (less than six months of age).  This is also why we may recommend retesting your dog in six months as a dog with immature heartworms will have a negative test.

Testing cats for heartworm disease is not as straight forward.  Cats generally have heartworm infections involving just a few worms.  These worms may be all males and not produce the protein we test for, or the cat may have so few worms that not enough of the protein is produced to cause the test to give a positive result.  Because of these factors, we may recommend a second test with cats that tells us if they are producing antibodies to the worms.  A positive on this test tells us the cat has been exposed to heartworms at some time in its life, but does not definitively tell us if the cat currently has an active heartworm infection.

There are many products available for heartworm prevention.  All the products made in the U.S. and regulated by the FDA are prescription products.  So by law, we must have seen your pet and performed a physical examination within the past calendar year to prescribe them. 

Buyer beware of purchasing heartworm prevention from sources other than your veterinarian.  The companies who manufacture heartworm prevention provide us with a guarantee that the product will be effective.  That guarantee does not apply to product purchased elsewhere. I personally have seen multiple dogs having heartworm infections whose owners purchased prevention via the internet. 

The American Heartworm Society released a study last month which showed an increase in the incidence of heartworm disease since a similar survey in 2004.  This study shows that there are a large number of infected animals out there.  All it takes is one mosquito to bite one of these infected animals and then bite your pet to spread this deadly disease.  A quote from the American Heartworm Society president Dr. Sheldon Rubin: “There is no reason a dog should have heartworm disease today.  If we can get more animals on prevention, we will get the numbers of heartworm-infected animals down.”

Spring Oaks carries the following heartworm prevention products:
For dogs: Given orally every month.
Triheart: Ivermectin/pyrantel
Heartgard Plus: Ivermectin/pyrantel
Interceptor: Milbemycin oxime

For cats:
Advantage Multi: monthly topical imidacloprid and moxidectin
Heartgard Plus: Ivermectin/pyrantel
Interceptor: Milbemycin oxime

Frequently Asked Questions:

Q: I can purchase Ivermectin at the feed store.  Can’t I just give that to my dog? 
A: The appropriate dosage of heartworm prevention for dogs is 0.006 mg/kg monthly.  Since the cattle Ivermectin is typically 10mg/ml it is very difficult to dose a dog appropriately.  For example, a 30kg Labrador Retriever’s dosage would be 0.018 mls (a very small volume for a 75 pound dog).  Ivermectin toxicity can cause tremors, dilated pupils, blindness and gastrointestinal signs (vomiting/diarrhea).

Q: I have read/heard that heartworm prevention is toxic to dogs.  Why should I give my dog something that may harm him/her?
A:  While some herding breeds of dogs such as the Collie may be deficient in a particular gene that makes them more sensitive to Ivermectin, at the very low dosage recommended for heartworm prevention this medication is safe for dogs and cats.  A little known fact is that Ivermectin is actually derived from a natural substance found in a bacteria (Streptomyces avermitilis).  It is also used in the control of River Blindness in people in Africa. 

Q: Why do you test for heartworms yearly?  My pet never misses a dosage of prevention.
A:  While heartworm prevention is very effective (most clinical trials show 94-100%), heartworms cause such devastating disease in animals we want to make 100% sure your pets do not get them.

Q: Heartworm prevention is expensive so why should I buy it? 
A: It will be more expensive in the long run not to give your pet prevention.  For a 75 pound Labrador Retriever an estimate of heartworm treatment would run greater than $600.  Your pet would have to be confined at home for 8 weeks and may have long term scarring of the lungs from heartworm disease.  A year’s supply of the prevention for the same Labrador runs between $6.83 to $8 per month.  How can you afford not to keep your pet on heartworm prevention?

If you have any further questions about heartworm disease or prevention, please schedule an appointment with Dr. Alshouse or myself.

Sincerely,

Dr. Jim Jackson