Neck Threadworm - When the itch isn't The Itch
- May 28
- 3 min read
Onchocerca cervicalis. Have you heard of this? According to this article 25% to 100% of horses have it. This parasite -neck threadworm - lives in the nuchal ligament (connective tissue) that runs from the poll down the neck. The adults can live for 10-15 years and can grow up to 30cm long. While the adult parasites don’t tend to bother horses - they tend to calcify around the parasite - their larvae cause intense itching on the head, neck, mane, and wither.
What are Neck Threadworms?
Neck threadworm is a nematode. This parasite spreads via biting midges, which are the same bugs that cause Queensland Itch, or Sweet Itch. The horse scratches where there is the most larvae, rubbing it bare, often creating a wound - the bugs then feed on that exact area, taking in the larvae and then spreading it to other areas in the same horse, or to the next horse.
In terms of symptoms, horses with neck threadworm and Itch will both have lesions on the neck (mane), head, and wither. Usually when it’s Queensland Itch alone, they will also scratch around the tail head. When it's neck threadworm alone, they will also scratch under the belly.
Horses can have both Itch and neck threadworm simultaneously.
Neck thread worm can migrate to the eye causing a lot of damage. In humans a different strain of this parasite causes ‘river blindness’.
You can treat neck thread worm with ivermectin. You can expect intense itching for 24 to 72 hours after treatment, and sometimes small weepy spots along the neck. There are also reports of ventral edema (a fluidy lump at the centre of the belly).This research suggests that ivermectin and moxidectin are both effective. Bear in mind that ivermectin is generally much cheaper. You would also not double-dose moxidectin - only ivermectin. Moxidectin is also the dewormer that will treat encysted strongyles (an intestinal parasite), whereas ivermectin only treats adult strongyles, and many parasites have developed a resistance to ivermectin and other anthelmintics in horses. That means if you are hoping to combat neck threadworms and intestinal parasites at the same time, you will need moxidectin.
We would encourage you to read the articles below. While they all recommend ivermectin - they each suggest different schedules. The consensus seems to be a double-dose of ivermectin two weeks apart. Ivermectin is very safe, with high tolerances, so we’re talking a whole tube for most horses, and then another whole tube 2 weeks later.
Some articles suggest that after the initial dosing you continue administering ivermectin every six weeks during midge season - which is mostly spring/summer while symptoms persist. Others suggest that you can apply the ivermectin worming paste topically, directly on to the lesions on the neck area.
This research suggests that ivermectin and moxidectin are both effective. Bear in mind that ivermectin is generally much cheaper. You would not double-dose moxidectin - only ivermectin.
Moxidectin is also the dewormer that will treat encysted strongyles (an intestinal parasite), whereas ivermectin only treats adult strongyles, and many parasites have developed a resistance to ivermectin and other anthelmintics in horses.
That means if you are hoping to combat neck threadworms and intestinal parasites at the same time, you will need moxidectin.
Read our other articles about intestinal parasites here:
All horses benefit from having a robust immune function to help them resist, combat and recover from parasites. Zinc supports immune function generally. Optimal zinc is in our Trace Mix. We have a chia-based mix and a zinc-based shampoo bundle that is very useful for helping to treat the symptoms of skin problems generally.
Treating with ivermectin does disrupt the gut biome.
You can support gut health with pre and probiotics. Bio Mos is only a 10g/day dose, making it great bang for buck, especially compared with other gut supplements on the market.
Here are some useful articles on neck threadworm:
(this is book version of the article above)
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