E. cuniculi (Head Tilt / Wry Neck) in Rabbits Encephalitozoon cuniculi (EC) is the most common cause of wry neck (head tilt) in rabbits. It’s a microscopic parasite shed in urine that attacks the brain, spinal cord, kidneys, and sometimes the eyes. Spores can survive for weeks in a contaminated environment. Signs: Head tilt, loss of balance, rolling, tremors, seizures, hindlimb weakness, increased drinking/urination, weight loss, cataract‑like eyes, or uveitis (usually one eye). Spread: Primarily through urine contamination of feeders, waterers, and housing. Can spread silently—healthy‑looking rabbits may still carry it. Control & Breeder Policy: Treat suspected carriers with fenbendazole (Safeguard®): 2 cc orally once daily × 28 days. Keep pens dry and urine‑free; disinfect feeders and waterers. Isolate or cull affected animals—nervous system damage is permanent, treatment won’t reverse it. Quarantine new stock at least 30 days before mixing. Bottom Line for Breeders: EC is highly contagious, hard to test for, and once signs show, recovery is rare. Quick action—quarantine or cull—is key to protecting your herd. The most common cause of head tilt (wry neck) in rabbits is infection with Encephalitozoon cuniculi (E. cuniculi or EC). About the Parasite Type: Microscopic, spore-forming parasite (phylum Microsporidia). Host: Domestic rabbits are the main host, but other animals (and immunocompromised humans) can be affected. Spread: Passed in urine; spores survive in the environment for weeks. Organs Targeted: Nervous system (brain/spinal cord), kidneys, and sometimes the eyes. Forms of Disease Subclinical: Rabbits with strong immunity may carry EC without obvious signs. Clinical: Weaker or stressed rabbits show symptoms that can be acute or chronic. Common Signs CNS (brain/spinal cord): Head tilt (vestibular disease), loss of balance (ataxia), rapid eye movement (nystagmus), weakness or paralysis, tremors, seizures, rolling. Kidneys: Increased drinking and urination, weight loss, kidney failure signs. Eyes: Cataract-like opacity, uveitis (inflammation), lens rupture, sometimes glaucoma. Eye signs are usually in one eye only. Diagnosis No single perfect test before death. Blood tests and urine PCR can help, but results are not always conclusive. Symptoms overlap with other diseases, so diagnosis is often presumptive. Treatment Fenbendazole (Safeguard®): 2 cc orally once daily for 28 days is standard in many rabbit programs. Anti-inflammatory meds may help with CNS symptoms. Damage to the nervous system is usually permanent; treatment can stop progression but rarely reverses it. Many breeders cull symptomatic rabbits to prevent suffering and limit spread. Prevention Cull or isolate infected rabbits. Keep hutches dry; remove urine promptly. Don’t share waterers, feeders, or bedding between groups. Quarantine all new rabbits for at least 30 days. References for Further Reading: Doboși AA et al., 2022. A Review of Encephalitozoon cuniculi in Domestic Rabbits. Pathogens 11(12):1486. Link Škrbec M et al., 2023. Encephalitozoon cuniculi Infection of Domestic Rabbits in Slovenia. Pathogens 12(4):516. Link