Each year, veterinarians do battle with an ancient enemy of our dogs and cats.  Heartworms are easily preventable with affordable and safe medications, but positive cases continue to rise.  Is there any hope that we could see an end to this parasite?

It’s been more than 150 years since a scientist discovered the heartworm parasite of dogs and more than 80 years since the parasite was found in cats.  Still, each year hundreds of thousands of dogs and cats are diagnosed with this dreaded worm and it is estimated that North American cases are actually in the millions.  In all this time, why have we not found a way to combat and stop this plague?

Heartworm disease is devastating to the pet’s health.  Spread by mosquitoes, this parasite can grow close to two feet long and takes up physical space in the heart’s chambers and pulmonary artery.  This means that the dog’s heart must work harder to push the same amount of blood out to the body.  Early signs of this disease included fatigue and exercise intolerance, but later signs can include coughing, fluid accumulation in the lungs or abdomen and death.

For cats, the heartworm larvae prefer the lungs and can cause vomiting, asthma like symptoms and even sudden death in some cases.

Not only is the pet harmed, but the owner is affected as well.  Heartworm treatments for small dogs can run in excess of $500 and costs for larger breeds might surpass $1200 or even $1500.  Sadly, the case might be worse for cats as there is no approved treatment for heartworms in our feline friends.


Amazingly, veterinarians do have an answer to this problem.  Safe, effective heartworm medications exist in a variety of easy to use applications.  What’s even more incredible is that the cost of a lifetime of preventive for most pets is significantly less than a single treatment for the disease.  So, why do pets continue to suffer and die from a preventable problem?

Two radical theories seen on the Internet state that either the heartworm medications are failing or that the parasites are developing a resistance to the drugs.  While conspiracy theorists may love these ideas, scientific evidence for both is lacking.  Heartworm preventives have a failure rate of less than 1 in 1 million doses.  Likewise, the complex life cycle of the heartworm does not lend itself to developing a natural resistance to medications.

Some people look to climate change for answers.  Increasing temperatures mean a longer mosquito season and larger potential for transmission to pets.  While we are seeing more mosquitoes in previously mosquito-free areas, the likely reasons are changes made by humans.  Irrigation of dry areas and increased plantings of trees in certain locales can actually help a mosquito population.  More mosquitoes mean more opportunities for transmission of heartworms.

When all the facts are reviewed, the simplest reason for our failure to control this deadly parasite is simply that we don’t give the preventive as we should.  Whether it’s forgetfulness or financial concerns, pet owners must realize that they are on the front lines in this battle and their actions could have dire consequences for the pet.

Thankfully, as pet owners, you do have powerful allies in this war.  Your veterinarian can help you pick the best heartworm medication for your pet and your lifestyle.  Oral formulations, like Heartgard and Sentinel, topical products, like Advantage Multi and even a long lasting injection, ProHeart 6, can help keep you on the winning side.

Beyond your veterinarian, veterinary pharmaceutical companies are also helping.  Websites, such as http://us.merial.com and email alerts are available to help you remember to give the preventive on time.


Don’t waste time looking for “natural” or organic ways to prevent heartworms; they simply don’t exist.  Follow recommendations given by your veterinarian and the American Heartworm Society (www.heartwormsociety.org).  It’s the best way to keep your pet and your wallet safe!  For more information on heartworms, visit www.MyVNN.com.  If you have questions about heartworm disease, products or treatment, visit the veterinarians at www.PetDocsOnCall.com.

Dr. Shannon Greeley is the Medical Director at Scottsdale Animal Clinic and can be reached at info@scottsdaleanimalclinic.com.