Taxonomy

  • Phylum Microspora; no mitochondria polar tube polar cap
  • Class Microsporida
  • Order Microsporidia
  • May be more related to fungi than to protozoa (Wasson and Peper 2000)
  • Obligate intracellular protozoan parasite
  • 52% normal healthy domestic pet rabbits arte infected (Keeble and Shaw 2006)
  • Ubiquitous in other species too

The life cycle

The life cycle of this coccidian is 3 – 4 weeks in total:

  • Inhaled, ingested or transplacental – rabbits of 4 – 6 weeks appear most vulnerable
  • In utero infections => invasion of foetal lens => => => => => => multiplication and euption of spores later in the rabbit’s life => cataracts, lens rupture and phacoclastic uveitis
  • Invasion of the mucosa per polar tube
  • Spiroplasm extruded and multiplication occurs in vacuole
  • Distribution by reticulo-endothelial cells => invasion of organs with high blood flow
  • Invasion of target organs
  • Intracellular multiplication, cell rupture (=> inflammation) and invasion of neighbouring cells or passage to circulation in 3-4 weeks
  • Shedding in urine 35 days after initial infection.

Presentations of Encephalitozoon cuniculi in pet rabbits

  • Granulomatous nephritis or interstitial infiltration of lymphocytes and plasma cells
    • Usually asymptomatic
    • Possibly haematuria
    • Incontinence could be neurological in origin
    • Treat with benzimidazoles and antibiotics
  • Pyogranulomatous phacoclastic uveitis
    • See treatment under iridal abscesses
    • Use topical ophthalmic preparations, parenteral oxytetracycline and a benzimidazole
  • Neurological manifestation of E. cuniculi infection: granulomatous encephalitis
    • Sometimes perivascular infiltration with lymphocytes and plasma
    • All areas of the brain
    • Torticollis
    • Treatment
      • Initial short-acting corticosteroids, parenteral oxytetracycline and benzimidazoles awaiting lab results
      • Vestibular agents

Transmission of Encephalitozoon cuniculi

  • Shedding in urine
  • Oral and tracheal access
  • Neonates can be infected but can also receive immunity from dam.
  • Ecto- and endo-parasites? May aid in transmission
  • Provision of recently cut short grass gathered from the wild

Pathology

  • Principal target organs are kidney, brain, spinal cord
  • Other target organs include liver and heart
  • Rupture of host cell => invasion of neighbouring cells => chronic, granulomatous inflammation.
  • In utero infections => invasion of foetal lens => => => => => => multiplication and eruption of spores later in the rabbit’s life => cataracts, lens rupture and phacoclastic uveitis

Survival of Encephalitozoon cuniculi in the environment

  • Survives in extreme cold or heat
  • At average temperature and in dry conditions it survives 4 weeks
  • Easily killed by routine disinfection

Diagnosis

  • Urine microscopy (35 days after initial infection)
  • Serology – antibodies develop soon after infection but clinical signs take much longer (several weeks)
  • Antibodies demonstrated 2 weeks before organisms can be demonstrated intracellularly and 4 weeks before histopathological changes are demonstrated in kidney or organisms demonstrated in urine (Harcourt Brown 2002)
  • PCR
  • CSF analysis
    • Procedure:
      • Propofol and intubation
      • Head flexed 90º to spine
      • 38mm 22G spinal needle in cisterna magna
      • 700-1000μl sample.
      • Vestibular signs are accentuated for up to 8hrs post sampling.
    • Findings
      • Lymphomonocytic pleocytosis 15 cells/μl (n=1.5 /μl)
      • Increased protein 0.79g/μl (n= 0.24g/μl)
      • Unfortunately other viral, protozoan or immune-mediated encephalitis may induce similar lymphomonocytic pleocytosis

Interpretation of Encephalitozoon antibody tests (Keeble 2007)

Single positive result in healthy rabbit

  • Recent infection prior to development of clinical signs
  • Chronically infected with no clinical signs
  • Previously infected and recovered
  • Antibody levels can persist for many years in symptomless animals

Single positive result in rabbit with clinical signs of encephalitozoonosis

  • Could be active Encephalitozoon cuniculi infection (or other infection causing signs)

Single negative result in healthy rabbit

  • Could be free from infection
  • Could be infected less than 2 weeks ago
  • Retest in four weeks

Single negative result in rabbit with clinical signs of encephalitozoonosis

  • Rules out Encephalitozoon cuniculi infection as the cause of clinical signs
  • Advise further tests
    • renal biopsy
    • CSF analysis
    • mononulear pleocytosis and elevated protein
    • MRI/CT scans

To establish an Encephalitozoon-free colony:

  • Test fortnightly for two months or until all animals are negative for a month, whichever is longer
  • Sacrifice any positive cases

Treatment

  • Albendazole 10 mg/kg q 24 hrs - ?teratogenic (Pollock 2006)
  • Fenbendazole 20 mg/kg q 24 hrs
  • Oxytetracycline 30 mg/kg SC q 72hrs.
  • Three possible therapies – my cocktail is albendazole and oxytetracycline as shown above.
  • Vestibular-calming agents
  • Environmental disinfection
  • Corticosteroids