Larval cyathostominosis?

[Kirikou]

I lost an older horse last Fall to what I now wonder could have been larval cyathostominosis. He had been doing really well for a while, but after being dewormed he suddenly dropped a lot of weight, developed acute diarrhea, a mild fever, and intermittent mild colic episodes. Vets were called immediately. They did bloodwork (which came back “wonky”), ran fluids, and managed symptoms as best we could, but nobody could quite explain what happened. With Winter closing in up here in the upper Midwest, and him severely underweight and uncomfortable within a couple months, we made the difficult decision to put him down. No necropsy at the time.

It’s only since reading up more after the fact that larval cyathostominosis crossed my mind. Fast forward to this Spring: his former pasture mates (all low shedders on fecals) were dewormed with Quest Plus in April, and several of them lost some weight afterwards, which has me questioning things again. The articles I’ve read suggest treating the cohort if a horse has confirmed or suspected larval cyathostominosis, and while I’ve got a call in to my vet, they’re more general large animal vets than equine specialists, and I like to do some “homework” before they call me back.

So, two questions for those of you who’ve dealt with this or know more:

1. Since moxidectin doesn’t have a 100% kill rate on ELs (and I know nothing really does), how would you follow up to clear suspected remaining encysted strongyles? If you saw some ongoing symptoms post-deworming (light diarrhea, digestive upset, weight not coming back as expected - which I have in one gelding now), how soon would you consider deworming again? Or would you take a different approach first?
2. Any good, current research or clinical resources you’d recommend reading? I’ve found a few articles, but would love to see some more.

Thanks in advance!

[Ghazzu]

Most recent AAEP recommendations here.

[Kirikou]

Thank you @Ghazzu!
I had this too but apart from a paragraph on page 19, it doesn’t really address larval cyathostominosis and relevant deworming:

“The efficacy of routine larvicidal treatments to reduce its risk is unknown. This makes assessing the prophylactic value of larvicidal treatments in populations of horses very challenging. Furthermore, the expected efficacy of a larvicidal treatment is substantially below 100%, with significant proportions of encysted larvae expected to survive treatment regardless of the anthelmintic. Larval reductions are also transient, with larval
counts rebounding within 5 weeks post-treatment (Nielsen et al., 2022a).”

I’ll try ordering that cited Nielsen article through my ILL system though.
Thanks again!

[Ghazzu]

Nielsen is pretty much The Guy wrt equine parasites.

[Ghazzu]

@Kirikou

I’ll try ordering that cited Nielsen article through my ILL system though.
Thanks again!

PM me an email and I’ll send it along.

[Kirikou]

Thank you SO much, @Ghazzu!

[JB]

@Kirikou

I lost an older horse

First, I’m so very sorry how old was he?

@Kirikou

The articles I’ve read suggest treating the cohort if a horse has confirmed or suspected larval cyathostominosis,

this isn’t really true. There’s no way (or desire) to eliminate large or small strongyles from the horse, as it’s the presence of a small burden which keeps the immune system on alert and managing the load on its own for about 80% of horses. So, 80% of horses won’t have a clinically relevant load

What was this guy’s deworming history? What dewormer did you use in the Fall? It IS possible he had a large enough encysted colony that using moxidectin, or possibly even a Power Pack, caused a big enough larval cyathostominosis issue as to cause all those symptoms. How soon after did all this happen?

@Kirikou

Since moxidectin doesn’t have a 100% kill rate on ELs (and I know nothing really does), how would you follow up to clear suspected remaining encysted strongyles? If you saw some ongoing symptoms post-deworming (light diarrhea, digestive upset, weight not coming back as expected - which I have in one gelding now), how soon would you consider deworming again? Or would you take a different approach first?

Generally speaking, the theory is that if there’s a substantial load, which usually also means a high enough FEC, if you target the adults, the encysted would emerge and you’d soon have a moderate or high FEC. Of course, that doesn’t address how to kill the EL if moxi or a PP isn’t effective enough, BUT, barring resistance, either of them should do a good enough job

Here’s a great article on all of this. I can’t tell when it was written, but it has references to some info from 2024 so it’s pretty current.

Larval cyathostominosis in horses - VETERINARSKA STANICA

In addition to what Ghazzu is offering, you might try contacting Dr Nielsen directly. I hear he’s pretty open to helping on interesting cases

[Kirikou]

Thank you so much! He was 23, and came from pretty “sketchy” circumstances. He got Fenbendazole when he first arrived in the Spring, and then Quest Plus in the Fall. Within 10 days after that Fall deworming, he started dropping weight really quickly, then developed intermittent colic signs, acute diarrhea, low-grade fever, etc. Had the vets out right away who gave fluids/supportive care, drew bloods multiple times (neutrophilia, decreased protein, and slight anemia) and couldn’t explain what ‘it’ was. They ruled out “worms” because he’d just been dewormed + fecal before the Fall deworming didn’t indicated much.

Thanks for clarifying the point about treating cohorts! I haven’t jumped to deworm his former herd again yet (since the April round), but I’m considering more gut support (pre/probiotics).

I’ll definitely read that article. Thank you for the link! And great tip about Dr. Nielsen. I might try shooting him an email if I don’t find enough info the linked articles you wonderful people sent!

Really appreciate your insight on this! Thanks!

[JB]

I’ll be really interested on Nielsen’s opinion on this. Protein loss is a symptom of cyathostominosis for sure. Does that mean that’s what it was? I have no idea