Heartworm Prevention


Q:  Why does one need a prescription for heartworm medicine?  Are we worried about our dogs getting infected or is it so veterinarians can bill us for an annual checkup?  When I was a kid we only took our dogs to the vet when they were sick.

A:  Your two questions raise different and unrelated issues.  Regarding the necessity of a prescription for heartworm medication, please refer to my post dated March 7, 2014 which explains the “Veterinary-Client Patient Relationship.”  With respect to you second question, “are we worried about our dogs getting infected?”  The simple answer here is “yes.”

The risk your pet has to heartworm differs throughout the United States, primarily the result of climate variations throughout the country.  Gulf states generally have the highest concentration of reported Dirofalaria Immitis (D.I.) infections in dogs.  This fact came to light in the aftermath of Hurricane Katrina, when 90% of dogs rescued from Louisiana and Mississippi, and relocated to western states, were tested for the female L4 stage of D.I. development and found to be heartworm antigen positive.  Even so, western states still do not have the same levels of annual D.I. infection as the gulf states and incidence levels vary from county to county.  The American Heartworm Society will release their 2013 D.I. Incidence Map this May.  Every year from 2000-2012 is available online for viewing.

My approach to heartworm is preventative rather than reactive.  I recommend all dogs and cats be treated monthly with flea prevention.  For dogs I recommend Trifexis, for cats, Revolution.  Both of these products contain a drug that prevents heartworm infection.  Regarding the use of Trifexis on a monthly basis – in one monthly oral administration, a dog receives an excellent primary flea adulticide (a significant issue in L.A. County), and the added benefit of monthly dewormer (G.I. parasites) coupled with excellent heartworm prevention.  All with very little risk of over-medicating or an adverse reaction occurring.

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