04/27/2026
FINAL STOP!
Today we make our last stop before we deboard our heartworm awareness month train, functionality junction!
We get this question countless times every year; why do I need to test for heartworm every year if I give my prevention on time every time?
The simple answer is this; an abundance of caution, and realism. How many times have you found your pets medication spat out on the floor hours, or even days, later? Who among us has never forgotten a monthly, or every three month dose? And finally, do you know anyone who can claim with absolute certainty that their dog or cat is 100% protected against parasites?
There is another factor in annual testing that is not often spoken about in clinic - the "retroactive" nature of heartworm preventative. Most oral heartworm preventatives (think Credelio Quattro, Simparica Trio, Heartgard, etc.) don't offer protection for the 30 days following administration. Rather, they treat and go after any heartworm larvae that have been present for the PREVIOUS 30 days! Anytime we miss or skip a dose, we open up the pet to infection for heartworms that may already be present.
Another crucial point is the time it takes for an animal to actually test positive on a heartworm test; it will take six months AFTER infection for your pet to test positive! When you factor in the retroactive nature of the prevention, the choice is remarkably easy; test annually, and prevent year round!
From the companion animal parasite council: "What's an acceptable number of heartworm cases in the United States? The answer is none."
