Here in Miami, though, it's always heartworm season. Indeed, no matter where you reside within the heartworm zone, diagnosing and treating these wormy villains is a year-long process.

The mosquito is the only known vector (transmitter) of the heartworm parasite, and dogs are its preferred host. While cats, and even humans, can "catch" heartworms, dogs are the critters for whom this parasite is uniquely adapted. In other words, human and cat immune systems will generally rebuff the parasite, while our dogs' will offer easy access.

To thwart these interlopers' efforts, veterinarians will always recommend monthly preventative medications for dogs who live in areas where mosquitoes have a presence. In more mosquito-rich areas, cats are also committed to monthly anti-parasite care (I strongly recommend it for all my feline patients, indoor or out).

This approach is obviously working. Dogs and cats are much less likely to become infected with heartworms if they're treated with monthly parasite killers. These drugs, designed to kill off the immature forms of the parasite before they can reach the disease-inducing adulthood stage, have historically been considered highly effective.

Lately, however, proof of our go-to drugs' spotty inability to tame these interlopers has shaken the veterinary world. For decades we have relied on their efficacy. Only now have we been treated to a perhaps somewhat belated indication of their inadequacies.

According to a recent panel of representatives from the American Heartworm Society and the Companion Animal Parasite Council, rumors of trouble in our parasite prevention approach have been confirmed. Our go-to drugs (macrocyclic lactones like avermectins and milbemycins) are reportedly less effective than they've ever been before.

To support such a claim, the researchers had to discount pet owner non-compliance as well as the influence of expanded mosquito migration and their wintry persistence –– both of which are significant factors in this disease's epidemiological study. And yes, in spite of these corrections, a "lack of efficacy" was definitively reported by the panel.

So what's a concerned pet owner to do?

Here's the answer from a panel member, Dr. Thomas Nelson, who spoke to the Journal of the American Veterinary Medical Association (JAVMA):

Until we get more data, until we get more answers, we really can't say more than to be sure to insist that we give the product every single month.
 

This is OK for now, but is unlikely to hold sway with the pet-owning establishment should a pet owner's diligent monthly prevention yield unsatisfactory results. The drug companies know this all too well, so you can be sure to expect new drugs along with new heartworm recommendations.

Stay tuned!

Dr. Patty Khuly

Pic of the day: My boy in pink by turquoise field