Friday, August 2, 2013

Veterinary Highlights: Change In Heartworm Guidelines For Dogs - No More Slow Kill

The Companion Animal Parasite Council (CAPC) has changed its guidelines for treatment of heartworm infections.

The CAPC now recommends against the slow kill method of heartworm treatment.

Heartworm cycle. Image CAPC

This change has been brought on by conclusively documented resistance to commonly used preventive medications in some heartworm populations in the Mississipi River Valley region.

The slow kill method should now be avoided.

This recommendation is supported by the American Heartworm Society. This is because continued usage of this treatment option would select for more resistant populations of heartworms, eventually making prevention difficult or impossible.

What is the slow kill method?

The slow kill method consists of a continuous treatment of a heartworm positive dog with a preventive, such as Ivermectin. The idea is that the Ivermectin keeps killing the microfilariae and larvae (baby heartworms). Over a two-year period, the adult heartworms should die off.

Should you want to use the slow kill method to start with?

The issue of creating resistant heartworm populations aside, is the slow kill method something you would want for your dog? Sounds better than injecting your dog with arsenic, doesn't it?

But perhaps it's not the best idea anyway. Listening to a Radio Pet Lady Network podcast with Dr. Donna Spector, DVM, DACVIM, a board-certified Veterinary Internal Medicine Specialist, on the subject, I'm thinking that the slow method is not something I'd want to use. Why?

The treatment of choice involves adulticide therapy, with medication (immiticide) that targets and kills adult heartworms.

And yes, that is an arsenical chemotherapeutic agent. Makes the slow kill method sound like an attractive option, doesn't it?

More over, this medication kills heartworm fast and the treatment involves strict cage rest for the duration of the treatment. This doesn't mean restricting activity, this means no activity at all. According to Dr. Donna, the dog should spend the entire treatment in a cage, period, and ideally should be carried out to potty. This is because while the adult heartworms are dying, there is a high risk with lung embolism with even moderately increased heart rate.

Pulmonary embolism and sudden death is the biggest risk with this treatment.

Why on Earth would anybody want to use this option then?

Here is the thing. This treatment, with all the risk and restrictions, goes on for a relatively short period of time. You know exactly when your dog is at risk, and you know how to minimize it.

With the slow kill method, the adult heartworms can die any time during the two year period.

You don't know when this is going to happen.

You will not have your dog sitting in a cage for two years. You're running the same risk, but with no predictability. If that wasn't bad enough, starting with a heartworm positive dog with no signs and no heart or lung damage, over the two years of the slow kill method, you're virtually guaranteeing the infection causing permanent lung and heart damage and injury. And this treatment is not 100% effective.

Does the slow kill method still look like such a good idea?

Listen to the podcast here.

Heartworm is a nasty disease, with treatment that is even nastier, no matter which way you slice it.

Diligent prevention is the ideal answer.

Source article:
New change in heartworm guidelines for dogs

Further reading:
Veterinary client noncompliance and heartworm resistance
Canine Heartworm Information and Recommendations
Don't Let Heartworm Become A Heartbreak! 
Veterinarians Answer: Heartworm Disease And Prevention
Reading About Heartworm Is One Thing; Watching A Dog Suffer Is Another


  1. Very interesting - I had no idea the guidelines have changed

    1. It's a very recent change. But the podcast was quite an eye-opener.

  2. I didn't know the guidelines had changed, either. We've been strict with our heartworm prevention over the years and have never had to treat a heartworm-positive dog, so although I knew *about* both methods of treatment, I didn't know the details of how each really worked. Thanks for outlining the differences! Both sound scary/risky, but I guess the while the risk is higher with the regular treatment than the slow-kill, it is almost more predictable and perhaps easier to mitigate.
    I pray that with good prevention, we'll never have to worry about it. But since we are getting more serious about taking on foster dogs, it may be something we'll need to know more about, as sometimes dogs in foster care are in need of heartworm treatment before they can be adopted.

    1. Pam, they just changed recently. There was talk before about the possibility of resistant strains, but it was not clear whether it was true resistance or result of improper compliance with the preventive.

      Now the resistance in the said areas has been proven conclusively, the guidelines have changed because of that.

      Prevention and regular testing is certainly the key.

      Do listen to the podcast, it's a great one.