WHAT IS NECK THREADWORM?On any ivermectin wormer you’ll see a list of parasites. At the end you will see the words Onchocerca Microfilariae, commonly known as neck threadworm. Like something out of a sci-fi movie, they live in your horse’s nuchal ligament. The nuchal ligament runs the entire length of the neck, from poll to withers and connects to the vertebrae. The majority of horses have neck threadworm. For most it doesn't present a problem, but some have a violent reaction to the resultant larvae or microfilariae. This is known as Onchocerciasis. The horse becomes itchy around the mane and tail, chest, shoulders and the midline of the belly.
Neck threadworm is a parasitic filarial worm that releases thousands of larvae during the course of its ten year life cycle. The larval form live in the horse’s skin, primarily around the mane and tail, head, shoulders, chest and mid-line of the belly, while the adult worm sets up shop in the nuchal ligament. The biting insect that serves as the larval carrier is the female culicoides fly, commonly known as no-see-ums, sand gnats and midges. These insects are also the cause of insect bite hypersensitivity, Queensland Itch, Sweet Itch and Summer Itch. Many cases of neck threadworm are misdiagnosed because they are assumed to simply be a result of itching due to the culicoides bite. In fact, the two are tied together in a three way vector between horse, culicoides and threadworm.