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Preventative Pet Health Care Series: Canine Heartworm Disease – The Mother Of Preventative Health Care In Dogs

Canine Heartworm

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Heartworm, also known as dirofilaria immitis, is a worm parasite that infects the hearts of dogs.  It is spread by the bite of a mosquito infected with its microscopic infective unit called microfilaria.  Thus, wherever there are mosquitoes, there is  a risk of heartworm disease.

Once infected, the microfilaria goes through several stages of development, emerging as an adult heartworm in 6 months.   Although the adult heartworm does not emerge for 6 months, however, once a dog is infected, the larvae are producing infective units that are transmissible to feeding mosquitoes and spreadable to other dogs within 10 – 42 days of infection.  Consequently, not only would your dog’s own health compromised by heartworm disease, once infected with heartworm, your dog would be a source of infection to spread to other dogs.

Once they reach adulthood, heartworms are constantly replicating, leading to significant infestation within one year.  As the worms travel back and forth from the right ventricle of the heart to the lungs via the pulmonary artery, they cause inflammation and damage to the heart muscle, the lungs, and the pulmonary artery. The end result of heartworm disease is right sided heart failure, clots, or both.

Treatment for heartworm, while necessary, carries risk.  Risks include reaction to the injectable arsenic based heartworm treatment, reaction to the dead worms and/or microfilaria, clot formation, or some or all of the above.  In my central Florida based veterinary hospital, we treat about 5-7 new cases of heartworm disease per month.

Luckily, heartworm is easily and safely prevented by administering a monthly heartworm preventive medication.  There are a number of heartworm preventive medications available on the market, the selection of which may depend on the unique health needs of the patient, individual tolerance, and/or cost.  Monthly heartworm screening is strongly advised as part of the yearly well visit.

Why is it necessary to do yearly heartworm screening for my dog when I keep him on year round prevention?

1.)    No matter how conscientious and owner may be, there is no such thing as 100% compliance.  Even being a few days late on heartworm preventive medication, a dog has the potential to become infected.

2.)    While heartworm preventatives are very effective, no protection is 100%.  Thus, a small percentage of dogs still become infected despite vigilant preventive administration.  These cases would continue unknown if regular screening was not performed.

3.)    Many heartworm preventative manufacturers will not guarantee the safety and efficacy of their products without a yearly heartworm test.

Dr. Roger Welton is the President of Maybeck Animal Hospital in West Melbourne, FL, Chief Editor of the Veterinary Advice and Information Website, Web-DVM, and founder/CEO of Dr. Roger’s Holistic Veterinary Care.

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