The Hidden Parasite That's Probably Causing Your Horse's Skin Problems
Why vets keep missing the most obvious cause of itchy, scratchy horses
If your horse has mysterious skin problems that won't go away no matter what treatments you try, you need to know about a little parasite that almost nobody talks about. It's called Neck Threadworm, and it's probably the real cause of what your vet is calling "allergies," "sweet itch," or "summer sores."
I've been around horses for over 70 years, and I've seen countless skin conditions get misdiagnosed and treated with everything from steroids to expensive salves. Most of the time, the real culprit is hiding in plain sight on the wormer box.
What Are Neck Threadworms?
Neck Threadworms go by the scientific name Onchocerca Microfilariae. You can find this name listed on most wormer boxes under the "effectiveness" section, but most people skip right over it.
Here's how these parasites work:
The adults live in your horse's nuchal ligament - that's the thick ligament that runs along the top of the neck and lets your horse raise and lower its head. Since this ligament isn't actually living tissue, most wormers don't reach the adult parasites living there.
The real problem starts when they reproduce. The young parasites (called microfilariae) migrate through your horse's tissue to reach the skin surface. This migration is what causes all the itching, scratching, and skin lesions you're seeing.
Almost all horses have them, but horses react differently. Some horses show no symptoms at all. Others develop severe itching and deep sores from constant scratching.
What Neck Threadworm Problems Look Like
The symptoms can vary wildly from horse to horse:
- Small raised bumps on the skin
- Bald spots of various sizes
- Intensely itchy areas that get rubbed raw
- Sores that appear in clusters or spread out randomly
- Problems that can show up anywhere on the horse's body
- Horses that seek out things to scratch against
- Skin conditions that come and go for no apparent reason
Sound familiar? That's because these symptoms get blamed on everything else under the sun: allergies, sweet itch, summer sores, bug bites, you name it.
The Eye-Opening Facebook Story
Real Case Study
A few years ago, someone posted in my Facebook group about a mare that was covered in itching sores. This horse was so miserable she was dragging herself through brush trying to get relief. The sores were all over her body, and she was nearly impossible to handle because of the constant itching.
The owner had tried everything the vet suggested. Nothing worked. Other horse people offered advice about allergies and various treatments. Still nothing.
Finally, someone in the group suggested Neck Threadworms and recommended a double dose of Ivermectin for four weeks.
The desperate owner decided to try it. She gave the mare two tubes of Ivermectin, and within less than a week, the mare showed dramatic improvement. Soon she was completely back to normal.
That got my attention.
My Own Testing
I started looking around the barn where I was working and noticed several horses with suspicious-looking spots on their faces, necks, shoulders, and hips. Most called them "allergies," some insisted they were bug bites. A couple of horses had rubbed deep sores on their bodies.
Now, I'm not one for randomly worming horses without good reason. I know what can happen when you kill off a massive parasite load too quickly - it can actually kill the horse. But I also knew that Ivermectin is one of the safer wormers to use.
I did some research and found that you'd have to give a horse a lot of Ivermectin tubes to reach a dangerous level. Since the wormer box specifically said it was effective against Onchocerca Microfilariae (Neck Threadworms), I decided to test my theory.
I grabbed a handful of Ivermectin tubes and double-dosed a couple of the horses with the worst skin conditions.
The results were dramatic. Their skin lesions started clearing up within a day or two, while the untreated horses' conditions continued unchanged. I treated the other affected horses and got the same quick results.
It only took one double tube dosing, by the time the week rolled for an additional dosing, all the lesions had dried up and were well on their way to healing.
Pretty convincing evidence, wouldn't you say?
My Results Over the Years
For the last few years, whenever I see a horse with a skin condition, the first thing I reach for is the wormer box. I can't recall a single time when proper Ivermectin dosing didn't stop the "sweet itch," "summer sores," or "allergies" in their tracks.
I'm not saying that real allergies and other skin conditions don't exist. But I seriously doubt they occur anywhere near as often as they get diagnosed.
Why Nobody Knows About This
Here's what's frustrating: very few people - including many veterinarians - are aware that Neck Threadworms are probably the most common cause of horse skin problems.
Suggest Neck Threadworms as a possibility, and you'll immediately get pushback. People want to blame allergies, sweet itch, bug bites, or anything else. They'll keep treating the outside of the horse with expensive potions and salves instead of addressing the real problem from the inside.
The Simple Solution
Treatment Protocol
Ivermectin at double doses for four weeks.
Here's what you need to know:
Check the wormer box - Make sure it lists "Onchocerca" in the effectiveness section. Most Ivermectin products do.
Double the normal dose - If your horse normally gets one tube, give two tubes. Do this every two weeks for four treatments total.
Be careful with unknown worming histories - If you don't know when your horse was last wormed, or if you suspect a heavy parasite load, consult with a vet first. A massive parasite die-off can be dangerous.
Watch for improvement - You should see results within a few days if Neck Threadworms are the problem.
Why This Works When Other Treatments Don't
Think about it logically. If your horse has itchy skin caused by parasites migrating through the tissue, no amount of external treatment is going to fix the root cause. You can put salves and steroids on the symptoms all day long, but until you kill the parasites causing the problem, the symptoms will keep coming back.
Ivermectin kills the microfilariae as they migrate through the tissue. No migrating parasites, no itching, no scratching, no sores.
The Bottom Line
Before you spend hundreds of dollars on allergy testing, special feeds, medicated shampoos, or prescription treatments, try a $20 solution from the wormer aisle.
I've seen this simple treatment work on horse after horse that had been suffering from "mysterious" skin conditions for months or even years. Owners who were at their wit's end suddenly had comfortable, happy horses again.
The most disturbing part? This information has been available forever. The wormer boxes have listed NeckThreadworms - Onchocerca for decades. But somehow, this obvious solution keeps getting overlooked in favor of more complicated and expensive treatments.
A Word of Caution
Safety First
Always use common sense when worming. If your horse has never been wormed or has an unknown history, consult with a veterinarian first. And if the Ivermectin treatment doesn't show improvement within a week, then you might actually be dealing with allergies or another skin condition.
But in my experience, most of the time you'll be amazed at how quickly your "allergic" horse becomes a comfortable, happy horse again.
Sometimes the simplest answer is the right answer. And sometimes that answer has been sitting on the wormer shelf all along.
Have you tried this treatment on your horse? I'd love to hear about your results. Contact me or join the discussion in my Facebook group.