More Musings on Heartworm

Rowley is now finished with the ‘adulticide’ heartworm treatment protocol:  he had two shots of Immiticide on successive days on June 14 and 15.  This is to kill the adult heartworms that were not dispatched by the first Immiticide shot that he received on May 15.  Meanwhile, any microfilariae that might find its way into his bloodstream is killed by the monthly dose of Heartgard that he receives and will receive until the weather no longer supports mosquitoes or microfilariae.

I’m pretty happy that we’ve gotten to this point, but there’s still so much I don’t know and can’t know, and my frustration really hasn’t abated much.  Any notion I had of a return to ‘normal’ life this month – resuming agility classes, going to the nature preserve for off-leash hikes – was banished when my vet, who is a cautious soul, said he wouldn’t okay any of that until we get a negative heartworm test on Rowley, and that would be October at the earliest.  WHAT?!?!  I just gave you two months of our best weather, now you tell me it’s still boring old leash walks and nothing else until the fall?!

Yeah.  And that’s because we are still living in fear of the real monster in this horror flick:  the pulmonary embolism caused by the corpse of a worm.  Disgusting?  Oh yeah.  A real possibility?  Yep, that too.


I can’t count the number of people who have thought that Rowley can somehow excrete the dead worms, as he would tapeworms or whipworms.  No.  Not possible.  These worms have been living in his pulmonary artery, which is not connected to his gut and digestive system; when they are killed off by the Immiticide shots, the bodies decompose and get reabsorbed by his body, mostly by his lungs.  So in order to accurately gauge the risk of a pulmonary embolism, I have to know how many worms there were, and how big the pieces of dead worms are that now float around in my dog’s body.  I can’t get that information anywhere!  I sent a questionnaire to “WORMS C/O ROWLEY” but got no response.  Worms don’t answer surveys.  Someone suggested that an x-ray might show the worm population in the pulmonary artery:  it won’t.  There is simply no way to know what is going on, so we have to proceed with the greatest amount of caution possible.

A negative heartworm test will tell us that not only are there no more live heartworms in residence, but there aren’t any worm corpses, either.  That’s because the antigen test for heartworm looks for a hormone that’s found in the skin of female heartworms, alive OR dead.  (There is no test that detects male heartworms.  Isn’t that odd?)  And that’s why, although the Immiticide shots killed the worms pretty expeditiously, it might take up to six months to get a negative heartworm test, as bits and pieces of dead worms could be decomposing slowly in there.  I’d be inclined to think that the longer time periods are due to a heaver load of heartworms, but who the hell knows?!

So as I put on Rowley’s leash for another walk and miss another agility class, I reflect again on the idiocy that kept me from giving heartworm preventive.  And let me just say that if I read the asinine quibble that “it’s not preventative”, I will go nuts.  Like this utter nonsense from Dogs Naturally Magazine:

Heartworm meds do not, by the way, prevent heartworms. They are poisons that kill heartworm larvae (called microfilariae) contracted during the previous 30-45 days.

Yes, you fool, and by killing the microfilariae it PREVENTS THAT MICROFILARIAE from migrating to the pulmonary artery and maturing into a heartworm!

From the VCA website:

The life cycle begins when a female mosquito bites an infected dog and ingests the microfilariae during a blood meal. The microfilariae develop further for 10 – 30 days in the mosquito’s gut and then enter its mouthparts. At this stage, they are infective larvae and can complete their maturation when they enter a dog. The infective larvae enter the dog’s body when the mosquito bites the dog. They migrate into the bloodstream and move to the heart and adjacent blood vessels, maturing to adults, mating and reproducing microfilariae within 6 – 7 months.

Yeah, I’m pretty sure that killing microfilariae IS preventing heartworm.

So here’s the thing:  if you’re buying (literally or figuratively) any of the BS on the internet or elsewhere about how your dog doesn’t need heartworm preventive, and if you live in an area where you have warm weather and mosquitoes at least part of the year, then you’re deluding yourself.  And if you’re saying to yourself ‘well, if my dog tests positive, I can treat it with herbs’, then you’re completely batshit crazy.  Your friends might not tell you that, but I will.  If your dog tests positive, your dog HAS WORMS LIVING IN HIS PULMONARY ARTERY.


How, pray tell, do you plan to get rid of those worms?  And how do you plan to dispose of the bodies?  Hmmmmm?  If you tell me you would let the worms die naturally, in the ‘slow kill’ method, then someone ought to confiscate all your dogs for their own safety.  You’re really going to let your dog live with worms in his heart?  Have any idea what that does to his organs?  Think about it.

If you’re going to tell me, as one friend did, that you hate to give your dog pesticides on a regular basis on the off-chance that they might need those pesticides at one time, then I understand that, and I say to you:  You have to think of it as insurance.  I pay homeowners’ insurance premiums faithfully every year.  I may never need to make a claim on that policy – I sure hope I don’t!  But the day that 150-year old oak tree comes crashing through my porch roof and demolishes half of my living room, I’m sooooo thankful that I didn’t ‘save’ money by canceling that insurance policy!  And so it is with heartworm preventives:  the one time your dog gets chomped by a mosquito carrying heartworm microfilariae, it will be the smartest decision you ever made to give him Interceptor every 6 weeks for 8 months of the year.  Unlike the oak tree that announces its presence in your house, you may never know that your heartworm insurance paid off.  But as climate change brings more and more weather aberrations to all parts of the country and more parasites establish themselves in areas that never hosted them before, I can tell you that your insurance is more likely than not to be needed, and sooner than you think.


5 thoughts on “More Musings on Heartworm

    1. It’s been shown that Interceptor or Sentinel, in which the active ingredient is milbemycin oxime, seem to kill microfilarae that are up to 45 days old, so many people give those preventives every six weeks.

      Here in Chicago, we typically have winters that feature periods of brutal cold, during which heartworm microfilarae cannot survive, so I would not give preventive in those months; but a mild winter, which climate change has made a real possibility, would probably cause me to keep on with the every six week dosing.

      I think a lot of the factors have to be considered in the light of what climate change is doing to our weather systems AND to the survival ability of pests and parasites.

      Also, if you do give chemical preventive — and I do now — you won’t be able to claim reimbursement for treatment costs from the manufacturer, should your dog ever test positive while on the preventive, unless you have given it per their instructions: that is, at full dose and at 30-day intervals. That’s a factor that some people will consider too.

      Liked by 1 person

      1. That’s interesting, thanks. As much as I would like to do away with chemical dewormers and flea/tick repellents, like you I realize that heartworm is no joke and there’s just no way I would stop treating for it, I won’t take that risk. As for the flea/tick thing, my dog seems to have a flea allergy, and Bravecto has been the only thing that’s kept her from constantly scratching all summer. 😦


  1. Flea allergies can make a dog’s life complete hell. I had a Sheltie girl some time ago who had a vicious flea-bite allergy. She got a lot of relief from natural hydrocortisone, which was soy-based and had the anti-inflammatory but not the immune-suppressing abilities of Prednisone. I don’t even know if that’s around anymore, I can’t find any mention of it on the ‘net. If I find any source for it, I’ll post it.


  2. Reblogged this on The Two Of Us and commented:
    I’ve heard all the scare stories about the evils of heartworm meds. I don’t like putting toxic chemicals into my dog’s body. But the fact of the matter is, heartworms are a very real thing, and treatment for and recovery from heartworms sucks. It’s up to every dog owner to weigh the risks and benefits of heartworm prevention meds based on their dog and where they live. But I give them to my dog, and this is why.


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