Heartworm Treatment Decisions

Here's a note from Pat:

I've read so much I am sick. Rescued my shih tzu mix 7 months ago.  He was tested negative for heartworms by agency's vet. My vet did not retest (though he did health exam) until 6 months later, and he is positive.

Vet gave me 2 options, suggesting we start with Heartguard. He has been on Trifexis since I have had him.

I read that the fast kill drug may or may not be available? And that dog has to be crated for up to 9 months.

I work and worry i wont be able to take care of him. And then he may die passing the worm anyhow.  I  cannot afford to leave him at vet for extended time.

Should i just put him to sleep? How do you keep a dog from exercising? Is my dog infectious to other dogs?  Does he need to be kept inside all the time?

I live in South Carolina.  What kind of life is that for a young dog?
How do I know what to do?

HOLY COW!  So many questions.  It's a complicated disease.  Here we go with some answers.

Hello, Pat,

Be calm. All is not lost.

If the dog tested negative 7 months ago, then you are looking at one summer's mosquito exposure, which probably does NOT equal very many worms.

If there are microfilaria (microscopic baby heartworms) present in the blood, then Heartgard is considered safer than the Trifexis (the active ingredient sometimes causes a reaction with the babies in the bloodstream).

Immiticide (the fast kill drug)is available. There was an older approach of just keeping them on Heargard, sometimes called "slow kill" or "soft kill". Now called "probably no kill", and not recommended. You just don't know if the worms will die any time in the next few years, and you're not going to be watching the dog closely and restricting its exercise for a few years.

After a dog is treated with Immiticide to kill the heartworms, we try to limit their exercise until the body has had time for the white blood cells to dissolve away the heartworm. This takes about 5 weeks. We
don't want the dog to have a rapid heart rate and higher blood pressure (from vigorous exercise), as that could shove the dead worms tighter into the artery, and maybe cause a blow-out of the blood vessel.

Most veterinarians are treating dogs in two stages now: a half-treatment of a single Immiticide injection, followed by the full 2-day treatment one month later.

Thus, you would need to restrict the exercise for about 9 weeks, not nine months.

Walking on a leash is fine. Being in the house if fine. Supervised in a fenced yard is okay. No running loose, and you don't encourage him to chase stuff. You do your best to make him a couch potato during this time. He doesn't have to be in a cage.

It is true that he could have bad complications when the worms die after the treatment, but the odds are in his favor, since he likely has very few worms. It is also true that if you don't treat him, there is a
remote chance that a worm could damage an artery and cause bleeding into the lungs.

If the dog is not very active, you could elect to just keep him on the Heartgard so that he doesn't get any more worms than he has. He might do okay with that, but I generally prefer to get them treated and cleared out.

The only way that the parasite is transmitted is via mosquito bites. Your dog may be a source of infection, but he's one of hundreds, so don't feel any guilt on that. If you locked him away, there would still be lots of sources of infection. You wouldn't be saving any other dogs.

It is very unlikely that you would need to leave him at your veterinarian for an extended time.

No, you shouldn't just put him to sleep. I'm guessing that everything seemed fine until you got the blood test. So everything is not that bad.

Your veterinarian who is actually seeing your dog is your best source of advice. Do not be ashamed to ask more questions until you feel like you have a good understanding of this complicated disease. If you don't let your doctor know you have questions, he/she thinks everything is hunky-dory.

4 thoughts on “Heartworm Treatment Decisions

  1. Dusty says:

    Hi Pat, I hope you didn’t let your dog sleep and I hope the worst is over, Curious to know the situation and how did you manage. What was the Vet advice. Looking forward to know more

  2. Cindy says:

    Hi Doc. We live in Arizona and have a 4 1/2 year old German Shorthaired Pointer that we rescued out of New Mexico 2 years ago. We recently discovered that he has heartworm (never had him tested before) and he was treated in mid-August with two shots of immiticide. We’re on week 4 1/2 now since his treatment, and while Fred has been pretty compliant with the exercise restrictions, he’s clearly getting bored with having to be outside on a leash and not being able to play with our other dogs. I understand from information posted on your site–which is great, btw–that it takes about 4-5 weeks for the worms to be broken down in his system. Our plan is to keep him on the leash through week 6, then let him in the back yard off leash and allow him to play with the other dogs after that. Does that sound reasonable to you? Are we out of the woods by now? He’s shown really no negative signs except for some cellulitis on his back near the injection site that appeared about day 10 and for which he was given 2 weeks worth of antibiotic. Our vet is great, but has seen few cases of heartworm in his career, so I thought I’d ask your opinion. Thank you so much for your help. The information on your site has been invaluable to us.

  3. Doc says:

    Hello, Cindy,

    Sorry about the late reply, but I was working at Scout Camp and no internet.

    By six weeks you really should be “out of the woods”. In rare cases, an artery weakened by the breakup of the dead worms can have problems when the dog returns to exercise. This can actually be bad enough to hemorrhage, coughing up blood. Again, this is rare.

    We usually recommend a gradual return to exercise, instead of going full-on right away. We also recommend close observation for the first few days.

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