E. cuniculi is a microsporidian protozoan parasite infecting a wide range of hosts. At least three strains have been identified on the basis of host specificity and other criteria.
It has recently been found to be more related to fungi than to protozoa.
Usually, no clinical signs are seen and approximately 50% of healthy domestic pet rabbits are thought to be infected.
The life cycle of this coccidian takes 3 – 4 weeks in total to complete:
The spore extrudes its polar tube and infects the host cell. It injects the infective spiroplasm into the cell where it undergoes extensive multiplication, which occurs inside a vacuole. Once the spores increase in number and obliterate the host cell cytoplasm, the cell membrane is disrupted and spores are released and free to infect new cells. Reticulo-endothelial cells are responsible for distributing the organism in the body, and organs with a high blood flow are commonly affected.
Shedding in the urine occurs 35 days after initial infection.
Transmission is usually via inhalation or ingestion of spores from contaminated tissues, food items or infected urine. Rabbits aged 4-6 weeks appear most vulnerable to infection.
Neonates can be infected trans-placentally but can also receive immunity from the dam.
Infection is usually asymptomatic, but clinical signs may include:
Neurological signs: incontinence, head tilt, obtundation, paralysis, seizures
Polyuria, polydipsia if the kidneys have been infiltrated
With in utero infections, there is invasion of the foetal lens and development of phacoclastic uveitis, cataracts and lens rupture.
Urine microscopy can be performed 35 days after initial infection.
Serology: antibodies develop soon after infection but clinical signs take much longer (several weeks). Antibodies can be demonstrated 2 weeks before organisms are found intracellularly and 4 weeks before histopathological changes are demonstrated in the kidney.
CSF analysis: will show lymphomonocytic pleocytosis, increased protein, but these are non-specific findings.
On post-mortem examination: principal target organs are the kidney, brain and spinal cord, but other targets may include the liver and heart. Lesions are often confined to the kidney and appear as focal, irregular, compressed areas, pale grey or white in colour.
Histopathology will reveal granulomatous lesions in the target organs, with periportal lymphocytic infiltration. Organisms can usually be readily demonstrated in the organs. In the kidneys, there is granulomatous nephritis or interstitial infiltration of lymphocytes and plasma cells.
Interpretation of Encephalitozoon serology
Single positive result in healthy rabbit
This may represent:
- Recent infection prior to development of clinical signs
- Chronically infected with no clinical signs
- Previously infected and recovered as antibody levels can persist for many years in symptomless animals
Single positive result in rabbit with clinical signs of encephalitozoonosis
- This could be an active Encephalitozoon cuniculi infection (or another infection causing the same clinical signs).
Single negative result in healthy rabbit
- This may signify that the rabbit is free from infection
- Or it may have been infected less than 2 weeks ago.
The rabbit should be retested in four weeks.
Single negative result in rabbit with clinical signs of encephalitozoonosis
- This rules out Encephalitozoon cuniculi infection as the cause of the clinical signs.
Further tests may be advisable, including CSF analysis, MRI scans or a renal biopsy
Usual treatment is fenbendazole daily for 4 weeks.
Albendazole has also been used for up to 10 days.
Oxytetracycline kills the parasite but care must be taken with causing antibiotic-induced diarrhoea.
Corticosteroids may be helpful in suppressing the inflammatory response and resolving clinical signs.
It is important to never guarantee a cure, as clinical signs may abate with treatment but may recur once it is stopped.
To establish a disease-free colony, screening and culling on positive cases can be performed, testing fortnightly for two months.
E. cuniculi is a potential zoonosis and immunosuppressed individuals should not come into contact with an infected rabbit.
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|Encephalitozoon cuniculi-associated phacoclastic uveitis in the rabbit: a review. Donnelly, T. M.; Veterinary Learning Systems, Yardley, USA, Journal of Exotic Mammal Medicine and Surgery, 2003, 1, 1, pp 1-3, 18 ref|
Sayers, I. (2011) Rabbit Medicine, E. cuniculi RVC Small mammal elective student notes
Baker, D. (2003) Natural pathogens of laboratory animals ASM Press
Percy, D. (2007) Pathology of laboratory rodents and rabbits John Wiley and Sons
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