Encephalitozoonosis in Cats (Felis) | Vetlexicon
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  • CauseEncephalitozoon cuniculi is thought to be a significant cause of neurological signs and renal failure in pet, meat, and laboratory rabbits (Oryctolagus cuniculus),  and an important cause of cataracts and lens-induced uveitis in the rabbit. The incidence in pet rabbits is so far unknown.
  • E. cuniculi is also a cause of uveitis and cataract in cats.
  • It is not known if infection with E. cuniculi alone is sufficient to cause disease, however it is undoubtedly able to cause disease in immunocompromised individuals.
  • Signs: uveitis, cataract, neurological problems, urinary incontinence.
  • Diagnosis: PCR, ELISA, serum protein electrophoresis, biopsy, histopathology and immunohistochemistry for spore detection.
  • Treatment: fenbendazole.
  • Prognosis: moderate for cats provided they can be treated; poor for neurologically affected rabbits.

Presenting signs

  • Cats: cataracts Cataract, uveitis.
  • Rabbits: neurological signs predominantly, urinary incontinence and renal failure.

Acute presentation

  • Rabbits: head tilt, collapse, paralysis, hindlimb paresis.

Geographic incidence

  • Unknown in the UK in pet rabbits, though thought to be relatively common. 
  • Very high prevalence worldwide in rabbits kept for meat (Lonardi et al, 2013 Neumayerová et al, 2014).
  • Worldwide seroprevalence in cats, with 2 to 6% of cats having antibodies to E. cuniculi.
  • Viable E. cuniculi spores have also been found in pasteurized cow’s milk and pork sausage.



  • E. cuniculi (previously known as Nosema cuniculi) is an obligate intracellular microsporidian parasite.


  • Central nervous system lesions produce signs related to focal non-suppurative granulomatous meningoencephalomyelitis and perivascular lymphocytic infiltration.
  • Ocular lesions appear to arise from protozoan spores deposited in the developing lens after vertical transmission in utero which, during the rabbit's life, erupt within and from the lens giving cataract and/or lens-induced uveitis from lens rupture.
  • Transmission is by oral consumption of urine infected with spores from the renal lesions caused by the organism in rabbits. Carnivores are infected by consumption of milk containing spores, and infected meat from rabbits, goats, horses, pigs, wild birds, etc.
  • Anecdotal reports of associated renal failure in rabbits have been made.
  • Inhalation of spores and transplacental infection is also thought to be possible.


Clinical signs

  • Cataract, uveitis (cats).
  • Neurological signs, urinary incontinence (rabbits).   

Confirmation of diagnosis

Discriminatory diagnostic features

  • PCR PCR (polymerase chain reaction) to detect Encephalitozoon cuniculi DNA is most sensitive on liquefied lens material and less sensitive using aqueous humour samples.
  • When sending a rabbit kidney for PCR, try to select a cortical lesion (will look like a pit in the kidney surface).
  • A positive E. cuniculi serology (by ELISA, western blot or, in the past complement fixation test) shows previous exposure but cannot prove current or ongoing infection. It provides good circumstantial evidence in the presence of appropriate clinical signs but in reality the only definitive test is a negative one, showing that E. cuniculi is NOT the cause of any presenting signs.
  • Serum protein electrophoresis showing an elevation in gamma globulins may support active granulomatous inflammation in the face of a positive E. cuniculi titer.

Definitive diagnostic features

  • E. cuniculi involvement can be proven by histopathology of neurological, renal or ocular lesions on post-mortem examination Post-mortem technique usually (focal non-suppurative granulomatous meningoencephalomyelitis and perivascular lymphocytic infiltration) or (in rabbits) renal lesions (pits and stellate scars on the cortical surface of the kidney caused by chronic interstitial nephritis). Conceivably these signs could be noted on laparoscopy and a kidney biopsy used for confirmation but this has not been reported in the literature to date.
  • Positive PCR of lens, fine needle aspirate, biopsy or post mortem material of a lesion is definitive proof of E. cuniculi being the causal agent; but a negative PCR does not necessarily rule out E. cuniculi, since it depends upon accurate material having been submitted and on the sensitivity of the laboratory test.

Laboratories for diagnosis of E. cuniculi

Gross autopsy findings

  • Renal lesions pits and stellate scars on the cortical surface of the rabbit kidney caused by chronic interstitial nephritis.

Histopathology findings

  • Histopathology of neurological lesions: focal non-suppurative granulomatous meningoencephalomyelitis and perivascular lymphocytic infiltration. 
  • Immunohistochemical staining for spore detection.

Differential diagnosis



Standard treatment


  • Fenbendazole (Panacur Rabbit 18.75% oral paste) Fenbendazole. For rabbits with clinical signs associated with E. cuniculi a treatment course of 20 mg/kg (1 syringe graduation per 2.5 kg bodyweight) daily for 28 days is recommended; for prevention the same dose is given for 9 days (Noah Compendium). Albendazole Albendazole has been shown to be effective in vitro but there is no albendazole product licensed for rabbits in the UK.
  • Oral albendazole and topical 1% prednisolone acetate Prednisolone for 8 weeks resolved an E. cuniculi intraocular granuloma.


  • Fenbendazole Fenbendazole is used to treat E. cuniculi infection in cats at a dose of 20 mg/kg once daily for 3 weeks (Benz et al, 2011).

Uveitis treatment (rabbit and cat)

  • Treatment for the clinical signs of anterior uveitis include topical steroidal or non-steroidal anti-inflammatory agents, parasympatholytic agents for ciliary spasm, to keep the pupil dilated, and to prevent posterior synechia. Posterior uveitis should be treated with systemic medications that will address the underlying cause.
  • Enucleation Eye: enucleation of blind, painful eyes not responsive to medications is a means to alleviate the animal's discomfort and to further diagnose the underlying cause (Colitz, 2005). Enucleation is required if the lens has ruptured. Provided blood pressure and hydration are normal, post-operative meloxicam Meloxicam should be given in both species to alleviate pain.
  • Phacoemulsification Phacoemulsification lens removal for lens-induced uveitis / cataract.



  • As oral consumption of urine is the mechanism of transfer, raising food off the floor is a useful method of reducing transmission in a colony of rabbits as is the use of sipper tube bottles rather than dishes or bowls of water.
  • Heat or steam cleaning will be the most effective methods for eliminating E. cuniculi spores.
  • Fenbendazole 20 mg/kg orally once daily for 4 weeks may be preventative for in-contact animals.
  • Test, isolate and monitor positive animals in a colony situation.
  • Keep immunosuppressed cats away from rabbit urine, feces, meat.
  • Any area used to prepare rabbit, pig, goat, wild bird meat should be cleaned with chlorine (household bleach), ensuring a contact time of at least 16 minutes, followed by rinsing with boiling water or steam.
Since E. cuniculi is a zoonotic infection, veterinary surgeons and nurses should wear gloves when dealing with infected rabbits or cats.



  • Not good for neurologically affected rabbits, ie clinical signs are advanced.
  • Reasonable prognosis for ophthalmic signs provided lens removal is undertaken and a full fenbendazole course given.
  • In acute infections urinary incontinence may resolve with fenbendazole treatment.

Expected response to treatment

  • Stabilization of neurological signs, remission of lens-induced uveitis signs.

Further Reading


Refereed Papers

  • Recent references from PubMed and VetMedResource.
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  • Sak B, Vecková T, Brdíčková K, Smetana P, Hlásková L, Kicia M, Holubová N, McEvoy J, Kváč M (2019) Experimental Encephalitozoon cuniculi Infection Acquired from Fermented Meat Products. Foodborne Pathog Dis 16(6), 394-398 PubMed.
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