We had a similar thing happen with our heeler-cross when he was about 3. He had been a stray, and was on HW preventative from when we got him at about 10 months, but apparently he’d already caught it and it wasn’t testing positive yet when we got him. They didn’t catch it for a year and a half. It was a light load, as he’d been on preventative the whole time.

So we went ahead with the ivermectin treatment for him, the first of three scheduled treatments. We brought him home, and I swear he almost died. He’s got to have some collie in him somewhere, because he was extremely sensitive to the treatment. He was disoriented, running into things, falling over, oceans of drool coming out of his mouth, it was so scary. Anyway, he made it through that.

We then consulted with our vet, who consulted with a canine heart specialist, and we all agreed that the best course of action was to see if the one treatment would work. (fortunately, this was possible as he’d been on HW preventative the whole time we had him, so there were no young HWs or eggs built up)

Anyway, the point I’m making is HW preventative is really important. It saved our dog’s life. Some vets will say you don’t have to give it through the fall/winter depending on where you live and how cold it gets, but down here in Texas it’s an every month thing for us. So be sure to keep that HW preventative up. It’s very important! Hope everything turns out ok!