Onchocerciasis (Neck Threadworm) in Horses: Causes, Symptoms, Treatment & Prevention
Constant neck and belly itch isn’t “just bugs.” Neck threadworms have a life cycle you can disrupt—with the right diagnosis, treatment, and barn routine.
Life Cycle & Causes
Adult Onchocerca cervicalis worms live in the nuchal ligament (crest of the neck). They release microfilariae that migrate through the skin. Culicoides midges ingest microfilariae while feeding and transmit them to other horses during later bites.
Risk Factors
- Warm, wet climates and seasons with heavy midge pressure
- Standing water, damp bedding, and poor insect control
- Horses with a strong hypersensitivity response to dying larvae
Symptoms & Diagnosis
- Itching (pruritus) and hair loss along the neck, chest, and belly
- Raised lumps or swelling over the nuchal area or ventral midline
- Scurf, crusts, and secondary skin infections from rubbing
Diagnosis: A veterinarian may perform skin biopsies/skin snips to look for microfilariae (often from ventral midline lesions); bloodwork and history (seasonal itch, response to deworming) support the diagnosis.
Treatment Options (Vet-Guided)
Antiparasitic & Anti-Inflammatory
- Ivermectin or moxidectin to kill microfilariae (your vet will set dosing and repeat timing)
- Anti-inflammatories to control reactions when larvae die (itch flare/“Mazzotti-like” response)
- Topical/antiseptic therapy if secondary infections are present
Comfort & Skin Support
- Rapid Relief Restorative Cream — thin, water-resistant barrier on clean, intact skin around irritated areas
- RESTOREaHORSE® Liqui-Gel — stay-put salve for localized comfort on clean, intact skin
- Draw It Out® Gel — targeted relief for sore muscles from chronic scratching
Apply topicals only to clean, intact skin. Stop and consult your veterinarian if irritation occurs.
Prevention & Environmental Management
Hygiene & Habitat
- Wash stalls, walls, mats, and trailers with SuperClean™ to reduce damp, organic build-up
- Fix drainage, remove standing water, and keep bedding dry
- Use fans/screens; adjust turnout to avoid peak midge hours (dusk/dawn)
Insect Control & Grooming
- Create a barrier with Citraquin® (see collection & How-To Guide)
- Regular grooming with the ShowBarn Secret® collection to remove sweat/dirt and spot skin changes early (safe for frequent use when rinsed thoroughly)
Long-Term Management & Complications
- Recurrent infections can predispose to uveitis (moon blindness) in some horses
- Monitor eyes for tearing, squinting, light sensitivity; protect from bright sun and dust as advised
- Schedule veterinary checks if itching returns seasonally—plan deworming and insect control ahead of peak midge months
Product Tie-Ins (Safe Use)
Insect & Environment
- Citraquin® 32oz | Full Citraquin® line | How-To Guide
- SuperClean™ for stalls, walls, mats, and trailers
Skin & Muscle Comfort
- Rapid Relief Restorative Cream (clean, intact skin)
- RESTOREaHORSE® Liqui-Gel (stay-put, clean, intact skin)
- Draw It Out® Gel for localized muscle soreness from rubbing/scratching
Topicals support comfort; they do not replace veterinary diagnosis, antiparasitic treatment, or infection control.
Onchocerciasis — FAQ
Will one deworming fix the problem?
Often you’ll see improvement after treatment, but some horses need a plan—repeat dosing/timing per your vet plus insect control and hygiene to break the cycle.
Is the condition contagious horse-to-horse?
Transmission requires midges (vectors). Focus on insect control and environmental management for the whole barn.
When should I call the vet immediately?
Severe or worsening itch, widespread hair loss, open/infected lesions, eye pain (tearing, squinting, cloudiness), or no improvement after treatment.
Educational note: This guide is informational and not a substitute for veterinary diagnosis or treatment. Always follow your veterinarian’s directions for deworming, anti-inflammatory use, skin care, and eye monitoring.
