Dogs Need Year-Round Heartworm Prevention

Dr. Dwight Bowman is a Professor in the Department of Microbiology and Immunology at Cornell University College of Veterinary Medicine. He received his Masters and PhD degrees from Tulane University in Parasitology.

He is also a traveling speaker with Heartworm University, an outreach educational program of the American Heartworm Society.

In this month’s Clinician’s Update, a supplement to the North American Veterinary Conference’s Clinician’s Brief, Dr. Bowman discusses the importance of administering heartworm preventives year-round.

Year-round heartworm prevention is the standard, regardless of where you live.
Year-round heartworm prevention is the standard, regardless of where you live.

Years ago, it was considered accepted practice in some northern United States to administer heartworm preventive during only certain months. Then, when the “cold” months were over, a blood sample was taken for a heartworm test. If the patient remained heartworm-negative through those cold months, heartworm preventive was restarted.

That old practice began to die out when monthly heartworm preventives became popular. It was simply too easy to give the medicine monthly, and the chance of your dog being bitten by an infective mosquito on a warm winter day simply put him at risk. Also, it was cheaper to continue prevention than it was to pay for an examination and retest.

Some pet owners even confused the old northern practice as being acceptable in the south. Here, however, three warm hours on a winter’s day and mosquitoes are out in force!

Now, there is yet another reason to continue year-round prevention. Read it in Dr. Bowman’s words:

“Today, heartworm is present in much of the nation. Because environmental and climatic factors influence mosquitoes and transmission of heartworm disease, it is becoming increasingly difficult to predict when mosquito season starts and stops; even in areas where seasonal changes appear to be definitive, some risk for off-season transmission can be a factor.

Because a single dose of heartworm preventives may not be 100% effective, and effectiveness declines with increasing time from infection via the mosquito bite, year-round administration of a preventive will minimize the risk for disease. In addition, placing dogs on year-round prevention provides the maximum protection when they travel to places with a different transmission time frame. Therefore, practitioners should encourage clients to follow a year-round prevention package that provides built-in internal parasite control coupled with flea and tick control.”

In his closing remarks, Dr. Bowman says, “The case for year-round prevention is strong–heartworm prevention should be built into a lifelong wellness and prevention program that reduces the risk for gastrointestinal parasite infection.”

These are strong comments from an expert, and Dr. Bowman is backed up by volumes of research and experience. Keep your dog on his heartworm preventive year-round, regardless of where you live.

See you Monday, Dr. Randolph.


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