Unlimited access >

Wanted to Share This Horse Care Experience- Neck Thread Worm

I have an 18 year old quarter horse gelding I have owned since he was a 2 year old.

In 2019, he put his leg over a concrete pony wall in our run in shed and through the wood wall. It was a pretty extensive injury with a wound that could not be stitched closed, a crazy amount of proud flesh, and partially severed tendons.

He actually healed very well considering the extent of the injury, but the following year I noticed issues that I believed to be unrelated to the injury that kept popping up.

He would develop girth galls very easily, even with custom fitted saddles and a variety of cinches. I swear I must have sent no less than 10 cinches back to Riding Wearhouse trying to figure this issue out.

He would also develop oozing sores on his midline that nothing seemed to help. You name it, I tried it.

His sheath swelled to the point it would never completely come down. I had the vet out of a thorough cleaning, and cleaned it frequently myself. Exercise would reduce the size quite a bit, but it never returned to normal. When this began and would not resolve, I hauled him to the largest equine clinic in the state, and they could offer me no good reason for the swollen sheath, except for maybe there has been lymph node damage from his run in shed injury. There recommendation was lunging him to help keep the swelling down, but there were still times I wondered how he could urinate as the sheath was that swollen.

And then there was the issue with his eyes. They would weep constantly, with tearing running all the way down his face. My vet checked his eyes, thought it was allergies and prescribed 15 generic Zyrtec twice daily. Allergies made sense as we lived in the South with fairly mild winters. But, the Zyrtec never truly stopped the eye watering. Fly masks did not seem to help, and he became an expert at destroying them, sometimes within an hour or two of puttting one on him.

Fast forward to last summer when we relocated back up North. When winter rolled around, I expected the eyes to clear up due to cold weather and a good, hard frost kill. Much to my dismay, nope, eyes are still watering with 30 Zyrtec per day.

I decided to start researching the eye issue, and one of the things that came up was Neck Thread Worm, formal name Onchocerca cervicalis.

Treatment for it was a double dose of Equimax dewormer, every two weeks for a total of 3 treatments. I called my former vet from down South, discussed what I thought was going on, and asked his opinion. His response was he did not see much Neck Thread Worm out in the field, so he kinda doubted that was it, but it would not hurt the horse to try it, so let’s do it.

The results were incredible. The horse is totally off Zyrtec and his eyes are not watering even with fly activity. I have ridden him more this year than in the near recent past with no girth galls or oozing sores on his ventral line.

What amazes me most is the swelling in his sheath is gone. It looks totally normal about 97% of the time. Occasionally it will seem slightly thicker, but nowhere near what he had experienced before.

I wanted to share this as it is the second time I have had a horse with a longtime issue, researched as much as I could, and worked with my vet to come up with a solution that was successful. I believe that as horse owners, sometimes we need to go with our guts and think outside the box. I trust my vets, but do not expect them to have all the answers. Sometimes by working together, we can solve problems that otherwise might not get resolved.

ETA- pictures.

December 2021

July 9, 2024

If you all are interested, I can also tell you about my horse who developed canker.


impressive research. you should write a letter to editor of one of the big vet journals and document your story. it would doubtless help many.


Yes please tell us about the canker.


This is fascinating, thank you!

I’d also love to know your canker story, having a horse who had canker surgery last June.


Wow. Thank you for sharing your experience.

What a difference. Poor boy must be so much more comfortable now.


In Spring of 2017, I noticed one of my geldings had a bulbous growth near the back of his foot. I had seen some pretty nasty cases of canker before, particularly on Amish farms and some kill pen horses. This was fairly small, but concerned me because if you touched it, it had a tendency to gush blood- enough blood that it would puddle on the aisle mats. It also seem to almost double in size fairly quickly, which I also knew was a symptom of canker.

Many people associate canker with horses standing in dirty stalls or excessive mud, but my horses are out 24/7 with access to a run in and areas on hills with great drainage and no muddy or mucky areas. My run in is cleaned out multiple times a day, and I had over this particular horse for 14 years and had never had any issues before.

I was using a barefoot trimmer at the time, and said something to her at our next appointment, and she was totally clueless and didn’t even know what canker was.

The vet was out at around the same time and I mentioned this lesion to him. He picked the foot up, looked at it for all of 10 seconds, put the foot back down, and said you need to take him to Tennessee Equine, and you need to do it sooner not later. I walked into the house in tears, figuring this would be the end for this horse, but immediately made the appointment to haul him into the vet hospital.

When he was seen there, they immediately confirmed it was canker, and recommended surgery. They would basically peel back and remove the entire sole of the foot, and much like a cancer surgery in humans, make sure they had clean margins with no infections. It would take approximately 90-120 days for the sole to regrow, so the horse would need to be stall bound for that amount of time.

Now this horse was not a great candidate for stall rest. We would go away to camp and trail ride, and it was not unusually for him to walk around his stall on his hind legs because he hated being stalled. I remember bawling like a baby thinking this was the end.

My husband, who has a doctorate in Animal Science, encouraged me to research alternatives, and not just casually, but to really dig. So, I started digging, and found some research tying canker to bovine papillomavirus. I also found research pointing towards bovine papillomavirus having a link to sarcoids as well. Research suggests horses kept near cattle had a greater chance of developing canker, and it could be spread by flies. If you think about Amish horses, many Amish farms also have cattle for either dairy or beef uses.

This particular horse had been a cutting horse futurity reject. I bought him as my “using horse” for cutting- my helper horses for other riders when they showed- and for trail riding. I had also lived on a dairy farm at one point with the horses, and my husband and I raise beef cattle. So yes, this horse had cattle exposure.

I started to look for information on any type of papillomavirus- human, bovine, canine and rabbits. I also looked for up to date treatments for sarcoids since there seemed to be a connection.

One product I came across was Xxterra, which is an herbal ointment made from bloodroot extract, that had shown some success in treating sarcoids. It is done directly on the lesion so it was something I could apply myself. I called the man who developed and manufactured Xxterra, and asked his opinion about using it for canker. He thought it was worth a try and had just had a conversation with a vet local to him who was just starting to try it on a horse with canker. The bloodroot extract is thought to stimulate the immune system to fight the canker and papillomavirus.

I spoke to my vet about how to prepare the foot, how to apply the Xxterra, and what to look for as far as something hurting the horse.

I cleaned the foot really well with betadine and a human nail brush, and really irritated the lesion so it bled. At this time it had many little bulbs that grew out of one another. I then cleaned it with peroxide and dried the foot well. I used a catheter tip syringe to apply XXterra into all the cracks in the bulbous areas and cover the entire lesion in the ointment. I then used a gauze pad to cover the lesion, then vet wrap, a diaper and duct tape.

I saw a difference the first time I unwrapped it about a day later. I would unwrap it, retreat it and wrap it again. It did cause the horse some pain when the pieces of canker started coming off, but he was never lame. I started treating him on June 10, and by July 1 you would have never known the canker had been there.

When my vet came out to examine the horse he was amazed at the results. He asked me what I planned to do if it came back, and I kinda looked at him and said surgery in a questioning way. He said nope, you do this again.

June 1, 2016

June 13, 2017

July 1, 2017


Very interesting! I texted a similar lesion on a dairy cow by basically burning it off with Wonderdust. It was not confirmed as canker, so we decided to treat it as nasty proudflesh. It took a while, Xxtera probably would have been quicker, but I didn’t think of it and the Wonderdust did work evenntually.

Bovine sarcoids suck. I’ve got a cat with one on her snout, so topicals have to be avoided. Azithromycin and cimetidine work to keep it at bay. Fwiw, in cats, surgery is absolutely contraindicated because no matter how clean the margins appear it will come back more aggressively each time.

Well done for doing the research and finding a great alternative for your horse!


Both of your experiences are enlightening, thank you for sharing!!!

I’ve used Xxterra to successfully treat sarciods in the past. Cool to see the results on your horse’s canker!


Sorry you went through this, but delighted by your research and thrilled that you had good outcomes. Thanks for posting.


There’s a lot of knowns about canker for sure. Moisture DOES seem to exacerbate or even be the final straw for it developing. It likely was in my case.

He’d cut his frog into his heel bulb on who-knows-what the Winter before finding his mass. It bled a lot, but didn’t make him lame, only very, very sore to treat, so I treated the best I could without getting my head kicked off. It was a WET Winter and Spring, even into the Summer (which was actually a blessing even as it was a huge pita). By Spring vaccination time, he was developing what I thought was just a mass of proud flesh, all on the back of his heel bulb, not on the frog itself. It bled a LITTLE, but not like canker often does, so I was utterly shocked when my vet looked and immediately said “I think it’s canker”. I opted for a biopsy, so we did that in the aisle, and that alone meant stall rest until the wound was healed enough and not likely to break open and bleed again (because the frog area bleeds like a MO’), and it was sent to NCSU’s pathologist. Her report came back with proud flesh and canker

Yeah, same, a sinking pit and on the verge of tears, having heard the horror stories, and personally knowing a horse who developed it in all 4 feet and it did her in :cry:

Yes, same here, and having had a horse who had a sarcoid removed from his side, I knew it was on the property. Our farm was an empty field when we bought it, and while it had been empty for many years, its previous life was a cow farm.

I never even ran into XTerra as a possible treatment but that’s fascinating! AND, it sort of makes sense.

I actually had surgery done, and not sure I’d do it again, but the mass grew quickly and I was able to take him to a local hospital with a surgeon who has seen a “lot” of canker (because it’s all relative). The weeks of stall rest following that were miserable, and trazadone was our friend for sure, but he was still unhappy and lost SO much weight :frowning:

the surgeon saw a lot of proud flesh, possibly some habronema involvement, and was really hesitant to say canker, and I was very conflicted between the pathology report which I expect was more accurate, after all they’re looking at cells, and his experience in canker surgery. So maybe there was just a hint of it left, and maybe the actual canker mass was 99% removed at the point of biopsy, so who knows.

That Summer was wet enough that even after the wound was healed, I still spent a lot of time wrapping his foot to keep it dry. No, there’s no guarantee that wetness brings it back, and the surgeon says he’s seen enough of it return despite utterly dry footing that he doesn’t scare people into being terrified of moisture. The blessing of the wet Summer was that there was PLENTY of grass in the small paddock around the barn I had to contain the horses in - stall rest horse would have FREAKED if the others left his sight, so they had to trade time out in the paddock and in their stall, and eventually all 3 were able to go into that paddock for some part of the day.

Now, to add to your xterra scenario - The Humble Hoof is a podcast with Alicia Harlov, and her episode on 12/9/23 was an interview with Dr Reilly on his thoughts, experience, history with canker, and treatments he’s successfully used to remove it without surgery, 100% success rate. The only failures were slacking of the owners OR, in a very few cases, recurrence 6-12 months later which he ended up addressing by supporting the immune system, in his words - " I’m just going to treat him like I do with EPM horses".

I HIGHLY recommend listening to it because he also talks about its pathology and what scenarios led to various topical treatments and why.