E. cuniculi in Rabbits UK — Encephalitozoon Symptoms & Treatment

According to the RWAF, Encephalitozoon cuniculi (E. cuniculi) is a microscopic protozoan parasite that infects rabbits throughout the UK. Studies suggest 30–50% or more of healthy rabbits carry antibodies — meaning they have been exposed.

The parasite localises in:

• Kidneys — often silently, causing scarring over time
• Brain — inflammation causes head tilt and balance loss
• Eyes — cataracts and lens inflammation (phacoclastic uveitis)

Carrying E. cuniculi is not the same as being ill. Disease flares when the immune system is stressed — by illness, surgery, poor diet, or social stress.

According to PDSA and the RWAF, transmission routes include:

• In utero — from infected mother to kits (most common)
• Urine — spores shed in urine; rabbits ingest from contaminated hay, bedding, or water
• Environmental spores — can survive weeks in damp conditions

Infected rabbits may shed spores intermittently without appearing unwell. Good hygiene reduces spread in multi-rabbit households but does not eliminate risk entirely.

Not all infected rabbits become sick. When disease develops, signs may include:

Neurological (most recognised)

• Head tilt (torticollis) — see Rabbit head tilt UK
• Rolling and inability to stand
• Circling to one side
• Hind leg weakness or paralysis
• Seizures (less common)

Kidney disease

• Increased thirst and urination
• Weight loss
• Lethargy
• Blood tests showing elevated kidney values

Eye disease

• White cataract in one or both eyes — often young rabbits
• Eye inflammation and cloudiness
• Lens rupture in severe cases

Neurological and eye signs may appear suddenly after months or years of silent infection.

According to the BVA, diagnosis is not always straightforward:

• Blood antibody tests — show exposure, not necessarily active disease
• Clinical signs — head tilt plus history strongly suggest E. cuniculi
• Urine PCR — may detect active shedding
• Response to treatment — improvement on fenbendazole supports diagnosis
• Imaging — CT or MRI in complex cases to rule out other causes

Your rabbit-savvy vet interprets tests alongside examination — a negative test does not always rule out disease.

There is no licensed cure, but fenbendazole (a worming medication) is the standard UK treatment:

• Course length — typically 28 days; repeat courses may be needed
• Anti-inflammatory medication — reduces brain swelling alongside fenbendazole
• Supportive care — syringe feeding, fluids, pain relief, gut motility support
• Eye treatment — if cataracts or uveitis present; surgery in selected cases

According to the RWAF, early treatment of neurological signs offers the best chance of recovery. Some rabbits retain a mild head tilt permanently but live comfortably.

Kidney damage from chronic infection may require long-term management — special diets and regular blood monitoring.

Many rabbits carry the parasite without ever becoming ill. Focus on:

• Stress reduction — bonded companionship, calm environment
• Hay-first diet and regular vet checks
• Clean, dry bedding — daily removal of soiled material
• Separate food and water for sick rabbits during active shedding if advised
• Monitor appetite and droppings daily

Discuss whether to treat in-contact rabbits if one housemate develops active disease — your vet will advise.

• Test before breeding if possible — discuss with your vet
• Avoid breeding rabbits with active neurological disease
• Hygiene in nurseries — disinfectable surfaces, separate litter trays
• Quarantine new rabbits before bonding
• Regular health checks — early kidney monitoring in at-risk rabbits

There is no licensed vaccine against E. cuniculi in the UK.