Diseases / List of Parasitic Diseases / Disease description:

Encephalitozoonosis in Lagomorphs (with a note on Bonobos)

Head tilt. Click here for full page view with caption Haed tilt. Click here for full page view with caption Phacoclastic uveitis due to Encephalitozoon cuniculi in the lens. Click here for full page view with caption Histopathology: Encephalitozoon cuniculi in a kidney tubule. Click here for full page view with caption Lens rupture and cataract due to Encephalitozoon cuniculi in the lens. Click here for full page view with caption Pitted kidney typically seen with Encephalitozoon cuniculi. Click here for full page view with caption

INFORMATION AVAILABLE

GENERAL INFORMATION

CLINICAL CHARACTERISTICS & PATHOLOGY

INVESTIGATION & DIAGNOSIS

TREATMENT & CONTROL

SUSCEPTIBILITY & TRANSMISSION

ENVIRONMENT & GEOGRAPHY

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General and References

Disease Summary

  • Encephalitozoonosis occurs primarily in rabbits but may also be diagnosed in rodents, cats, dogs, foxes, sheep, goats, pigs, primates, humans and also some avian hosts. The majority of infections are opportunistic in immunocompromised hosts. (B600.16.w16, B601.11.w11, B603.4.w4, B609.2.w2)
  • This parasite is also thought to be one of the causes of "fading puppy syndrome" and has been implicated as a disease-causing parasite on fox fur farms. (B603.3.w3)
Lagomorphs
  • Encephalitozoon cuniculi infection of rabbits often causes a chronic latent disease. (B614.10.w10)
  • The most commonly sites of infection are kidney, brain, spinal cord, liver, heart, and the lens of kits infected in utero. (B603.4.w4)
  • Encephalitozoon cuniculi can cause a granulomatous nephritis and encephalitis leading to chronic renal failure and/or vestibular disease. If infection has occurred in the kit in utero then rupture of the lens, pyogranulomatous uveitis and cataract formation may be seen. (B600.16.w16, B603.4.w4)
  • As well as encephalitis, nephritis and uveitis, encephalitozoonosis has also been associated with myocarditis, vasculitis, pneumonitis, hepatitis, splenitis, and spinal nerve root inflammation in rabbits. (B602.20.w20)

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Alternative Names (Synonyms)

  • E. cuniculi infection
  • Nosematosis
  • Encephalitozoon cuniculi infection
  • Nosema cuniculi is a synonym of Encephalitozoon cuniculi 

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Disease Type

Parasitic Infection

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Infectious/Non-Infectious Agent associated with the Disease

There are several species of Encephalitozoon but Encephalitozoon cuniculi is the most important species that is found in animals. (B600.16.w16)
Encephalitozoon cuniculi 
  • Encephalitozoon cuniculi is an obligate intracellular microsporidian (Microspora) protozoon parasite. (B600.16.w16, B601.11.w11, B602.20.w20, B603.4.w4, B609.2.w2)
  • The infectious stage of this parasite is a spore. (B602.20.w20)
  • Morphology: 
    • Mature spores are oval with a thick cell wall and approximately 2.5 by 1.5 Ám in size and stain positive with carbol fuchsin, Gram's, or Giemsa stains. (B602.20.w20, B603.3.w3, B609.2.w2, B614.10.w10)
    • When viewed with polarised light, the spores show green birefringence. (B602.20.w20)
    • The spores do not stain well with hematoxylin and eosin. (B614.10.w10)
In Lagomorphs
  • History:
    • "The disease was first described in 1922 as an infectious encephalomyelitis causing motor paralysis in young rabbits (Wright and Craighead, 1922), although other investigators had previously reported similar diseases in laboratory rabbits". (B614.10.w10)
    • Encephalitozoon cuniculi was later shown to also be a cause of head tilt in rabbits. (B602.20.w20)
  • Pathogenesis:
    • Infection occurs when a rabbit ingests spores in food or water that have been contaminated with infected urine. (B600.16.w16, B602.20.w20, B609.2.w2, J15.28.w1)
    • Spores may also be inhaled. (B600.16.w16, B601.11.w11, B602.20.w20, B603.4.w4)
    • The spores then infect the host mucosal cells (infection occurs when the spore's polar filament is used to inject the spore contents into a host cell (B602.20.w20)) where they multiply and mature within vacuoles. (B600.16.w16, B603.4.w4) The reticuloendothelial system cells (e.g. macrophages) also become infected and this can spread the spores to extraintestinal organs. (B600.16.w16, B601.11.w11, B602.20.w20, B603.4.w4, B604.5.w5, B609.2.w2)
      • Spores appear in the kidneys around thirty five days post-infection. (B604.5.w5)
      • The infection is terminated in the kidney between forty and seventy days, by which time lesions are starting to form in the brain. (B604.5.w5)
    • The vacuoles eventually distend and cause the cells to rupture releasing the mature spores into the bloodstream (where they can continue to spread around the body) or into the urine (if it is renal cells that rupture). A granulomatous inflammation develops at these sites of ruptured cells (primarily the kidney and brain) and is associated with the clinical disease that is seen. (B600.16.w16, B603.4.w4, B609.2.w2)
    • At the granulomatous inflammation stage there may not be any organisms present. (B603.4.w4)
    • In utero infection: Encephalitozoon cuniculi can be transmitted from the doe into the developing lens of the fetus. The replication of spores within the young rabbit's lens leads to cataract formation, rupture of the lens, phacoclastic uveitis (B600.11.w11, B609.2.w2, J541.7.w1) and possibly glaucoma. (B609.2.w2)
    • Immunocompetent rabbits will develop chronic, subclinical infections e.g., focal granulomas in the brain and kidneys. Resistance is T-lymphocyte dependent although antibodies will also contribute by resulting in opsonisation by macrophages and complement-mediated killing. Animals with CD4 T-lymphocyte deficiencies are reported to be particularly susceptible to microsporidian infections as are patients who are on immunosuppressive drugs. (B602.20.w20)

Infective "Taxa"

Non-infective agents

--

Physical agents

-- Indirect / Secondary

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References

Disease Author

Nikki Fox BVSc MRCVS (V.w103)
Click image for main Reference Section

Referees

John Chitty BVetMed CertZooMed MRCVS (V.w65); Aidan Raftery MVB CertZooMed CBiol MIBiol MRCVS (V.w122); Richard Saunders BVSc BSc CertZooMed MRCVS (V.w121); Dr David L Williams MA VetMB PhD CertVOphthal FRCVS (V.w133)

Major References / Reviews

Code and Title List

B600.11.w11, B600.16.w16, B601.11.w11, B601.12.w12, B602.20.w20, B603.3.w3, B603.4.w4, B604.5.w5, B606.13.w13, B609.2.w2, B614.10.w10
J3.152.w5, J29.5.w1

In Bonobos
J119.58.w1

Other References

Code and Title List

J3.158.w2, J4.127.w2, J19.84.w2, J21.28.w1, J24.75.w3, J31.26.w1, J32.151.w1, J83.9.w1, J83.11.w1, J354.5.w1, J541.3.w1, J541.7.w1

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Clinical Characteristics and Pathology

Detailed Clinical and Pathological Characteristics

General --

Clinical Characteristics

--
Lagomorphs
  • Most infections are actually asymptomatic or remain asymptomatic until the animal becomes immunocompromised with stress or debility or age etc. (B602.20.w20, B609.2.w2, J29.5.w1)
  • Ocular and CNS are the signs most commonly reported but this is mainly determined by the site of infection and the extent of the tissue damage. (B609.2.w2)
  • Signs may be nonspecific or neurological (CNS). (J29.5.w1)
Neurological

The prevalence of this parasite as a cause of disease of the central nervous system is controversial because it is not possible to gain a definitive ante mortem diagnosis and the post mortem lesions do not always correlate particularly well with the clinical disease. (B609.2.w2)

  • Vestibular signs are the predominate neurological signs and include:
  • Other: 
    • Hindlimb paresis (B601.11.w11, B603.4.w4, B609.2.w2, B614.10.w10)
    • Tremors (B601.11.w11, B603.4.w4, B604.5.w5, B606.13.w13, B609.2.w2, B614.10.w10)
    • Paralysis (B601.11.w11, B603.4.w4, B606.13.w13, B609.2.w2)
    • Urinary incontinence (B601.11.w11, B603.4.w4, B609.2.w2)
    • Stiff rear limb gait (B603.3.w3, B609.2.w2)
    • Altered behaviour (B602.20.w20, B603.4.w4) 
    • Seizures (B601.11.w11, B602.20.w20, B603.4.w4, B604.5.w5, B609.2.w2, B614.10.w10)
      • rabbits that have seizures are sometimes left blind or comatosed; however, others may recover completely. (B602.20.w20)
    • Collapse (B601.11.w11)
    • Coma (B606.13.w13, B614.10.w10)
    • Death (B601.11.w11)
      • Sudden death can occur. (J4.127.w2)
Ocular

Ocular lesions are usually unilateral and are seen as post-natal infections:

  • Iridial abscess (B609.2.w2)
  • Cataract (B600.11.w11, B601.12.w12, B609.2.w2, J354.5.w1, J516.60.w1)
  • Lens rupture (B609.2.w2)
  • Hypopyon (B609.2.w2)
  • Uveitis (including aqueous flare, hyphema, mydriasis) (B600.11.w11, B601.12.w12, B609.2.w2, J354.5.w1, J541.3.w1, J541.7.w1)
  • Photophobia (B609.2.w2)
  • Often presented to the clinician due to the owner noting a white mass in the eye, in the absence of any signs of discomfort or inflammation. (J541.3.w1)
Renal
  • Irregular pitted kidneys (this may not be clinically significant). (B601.11.w11, B609.2.w2)
  • If there is renal compromise/failure (which is unusual), this may lead to:
    • dehydration
    • depression
    • anorexia
    • cachexia
    • lethargy
    • gastrointestinal hypomotility
    • (B601.11.w11, B609.2.w2)
    (B601.11.w11, B609.2.w2)
  • Polydipsia, polyuria (B606.13.w13)
  • There may be a loss of litter training. (B606.13.w13)
  • Incontinence (B606.13.w13)
  • Urine scald (B606.13.w13)
Other 
  • General:
    • Neonatal deaths (B602.20.w20)
    • Retarded growth. (B601.11.w11, B604.5.w5)
    • Sudden death. (J4.127.w2)
  • Reproductive:
    • Abortion. (B602.20.w20)
  • Cardiac: 
    • There may be myocarditis but this is usually not apparent clinically. (B609.2.w2, B614.10.w10)
    • There can occasionally be a heart dysrhythmia. (B603.4.w4)
  • Hepatic: 
    • There may be a focal non-suppurative hepatitis but this is usually not apparent clinically. (B609.2.w2, B614.10.w10)

Incubation

--
Lagomorphs
  • Encephalitozoonosis is often latent in rabbits. (B614.10.w10)
  • Most infections are actually asymptomatic or remain asymptomatic until the animal becomes immunocompromised by stress, debility or age etc. (B609.2.w2)
  • Lesions do not occur for at least one month after experimental inoculation. (B603.3.w3)
  • Shedding of spores in the urine: 
    • Encephalitozoon cuniculi organisms localise in the renal tubular epithelial cells and this results in spores being shed in the urine six weeks after the initial infection. (B609.2.w2)
    • This shedding peaks at two months post infection and ends at three months post infection. (B609.2.w2)

Mortality / Morbidity

--
Lagomorphs "The true incidence of clinical disease is unknown". (B609.2.w2)
  • Most rabbits are asymptomatic. (B609.2.w2)
  • Up to 80% of rabbits tested serologically positive for Encephalitozoon cuniculi in Europe and the United States. (B609.2.w2)
  • In the UK, this disease is widespread in the domestic rabbit population - in clinically healthy pet rabbits the seroprevalence is thought to be around 52 %. (B601.11.w11, B603.4.w4)
  • Wild populations of rabbits are generally 100% negative. (B603.4.w4)

Prognosis and expected course of disease
Generally the prognosis for rabbits with encephalitozoonois is guarded. 
  • There is a varied response to medication and many cases improve with supportive care alone. (B609.2.w2)
  • Some rabbits have a waxing and waning course of disease progression. (B609.2.w2)
  • Owners should be made aware that some affected rabbits may require long term nursing care at home including syringe feeding and padded bedding in recumbent patients. (B609.2.w2)
  • Some rabbits recover without any treatment. (J3.152.w5)
In renal insufficiency or acute severe neurological signs
  • The prognosis is guarded to poor. (B609.2.w2)
  • Some patients may improve with supportive care. (B609.2.w2)
  • Note: many cases are poorly diagnosed. (V.w65)
In acute cases that present with urinary incontinence
In ocular disease
  • This is not likely to progress to renal or CNS disease. (B609.2.w2)
  • The response to medication varies. (B609.2.w2)
  • Glaucoma may be prevented by removing an affected lens by phacoemulsification. (B609.2.w2)
  • There is a good prognosis following the removal of the lens where necessary. (B601.11.w11)
  • Medical treatment of the parasitic infection, together with topical steroids to reduce ocular inflammation, can be effective and prevent long-term inflammatory sequelae. (B601.12.w12, J541.7.w1)
In severe muscular or neurological disease
  • There is often chronic debility. (B609.2.w2)
  • The residual deficits (particularly neurological signs) are very difficult to predict until after the therapy course. (B609.2.w2) Once neurological signs have developed, it is not likely that these signs will resolve completely. (B601.11.w11)

Pathology

--
Lagomorphs
  • Encephalitozoon cuniculi organisms may be seen on histopathology either intra- or extra-cellularly. (B614.10.w10)
  • In acute cases of infection, lung, kidney, and liver are reported to be affected. (B602.20.w20)
  • In chronic cases of infection, brain, kidney, and heart are affected. (B602.20.w20)
Nervous system
The characteristic lesion of encephalitozoonosis in rabbits is a granulomatous encephalitis. (B614.10.w10) Some cases may have a multifocal nonsuppurative granulomatous meningoencephalomyelitis. (B603.3.w3, B609.2.w2)
  • Gross pathology:  Brain lesions are not evident grossly. (B604.5.w5)
  • Histopathology:
    • Microgranulomatous lesions. (J29.5.w1)
    • Lesions can occur in all areas of the brain but there is often a perivascular and periventricular distribution. (B614.10.w10)
    • Commonly there are focal granulomas which are randomly distributed and characterised by a central necrotic area that is surrounded by lymphocytes, plasma cells, epitheloid cells, microglia, and occasionally giant cells. (B604.5.w5, B614.10.w10)
    • However, sometimes there may only be dense accumulations of glial cells. (B603.3.w3, B609.2.w2, B614.10.w10)
    • There may also be prominent perivascular cuffing with lymphocytes and plasma cells. (B602.20.w20, B603.3.w3, B604.5.w5, B609.2.w2, B614.10.w10)
    • A non-suppurative lymphocytic meningitis may also be seen particularly in areas that are closely associated with brain lesions. (B602.20.w20, B603.3.w3, B609.2.w2, B614.10.w10)
    • Numerous Encephalitozoon cuniculi organisms may be seen together in the central necrotic areas of the granulomas or they may be seen individually in the meninges or in areas of glial cell accumulations. (B614.10.w10)
    • Host cells may be seen greatly distended with Encephalitozoon cuniculi organisms and there is often no detectable inflammatory response. However, organisms from ruptured cells can initiate an intense cellular response. (B614.10.w10)
    • In a wild Sylvilagus sp. cottontail rabbit: (J4.127.w2)
      • Cardiac: several granulomatous foci. (J4.127.w2)
      • CNS: large diffuse areas granulomatous in brain regions from the thalamus to the pons, with severe lymphoid infiltration of the meninges and severe, sharply delinniated necrotising lesions in the thalamus and midbrain with adjacent oedematous parenchyma, increased numbers of capillaries and sometimes lymphocytes in Virchow-Robin spaces. (J4.127.w2)
Renal
  • Gross pathology
    • Early / acute stages of disease: 
      • The kidneys may be enlarged. (B604.5.w5)
      • Multiple, white pinpoint areas that are randomly scattered over the surface of the kidney (B614.10.w10); small white areas are seen in the cortex (B604.5.w5).These areas are due to the scars from the foci of granulomatous inflammation that the parasite causes. (B603.3.w3)
    • Chronic infection:
      • Small (two to four millimetres) indented grey areas on the cortical surface. (B604.5.w5, B614.10.w10)
      • If the kidney is extensively involved it may have a granular appearance. (B614.10.w10)
      • "multifocal, depressed areas of fibrosis pitting the surface of the kidney-usually an incidental finding". (B609.2.w2)
  • Histopathology
    • Microgranulomatous lesions. (J29.5.w1)
    • "Granulomatous nephritis or degrees of interstitial infiltration of lymphocytes and plasma cells with fibrosis and tubular degeneration and dilatation...The scars often extend from the cortical surface to the medulla". (B614.10.w10)
    • Renal tubular necrosis (B609.2.w2)
    • Interstitial nephrosis (B609.2.w2)
    • Lymphohistiocytic tubulointerstitial nephritis (B609.2.w2)
    • Encephalitozoon cuniculi organisms may be seen in the tubular cells (usually in the medulla) or they may be seen free in the lumens. One study demonstrated that rabbits with chronic interstitial nephritis and scarring had fewer organisms on histopathology then those with acute lesions. (B614.10.w10) Organisms can be seen with gram's stain. (B609.2.w2)
Ocular
  • Phacoclastic uveitis resulting from lens capsule rupture. (B601.12.w12)
  • Pyogranulomatous inflammatory deposit. (B600.11.w11)
  • Histopathology: A break, usually anteriorly, in the lens capsule, with a ring of giant cells and macrophages filled with lens material around this, and a band of fibrous tissue with lymphocytes and plasma cells around the granulomatous ring. Partial liquification of the lens cortex, and mild anterior uveitis (lymphocytic/plasmacytic). (J541.3.w1)
Liver 
  • A focal non-suppurative hepatitis. (B614.10.w10)
Heart
  • Myocarditis. (B614.10.w10)
Other
  • Vasculitis, pneumonitis, spinal root inflammation, and splenitis have also been reported in encephalitozoonosis. (B609.2.w2)

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Human Health Considerations

  • Zoonotic potential particularly in immunosuppressed humans. (B601.11.w11, B603.4.w4, B609.2.w2) 
    • Primarily people with AIDs. (B603.4.w4, B614.10.w10)
  • Clinicals findings
    • Encephalitozoonisis can cause diarrhoea, keratoconjunctivitis and renal disease. (B600.16.w16, B603.4.w4)
    • It has also been associated with peritonitis. (B614.10.w10)
  • Transmission
    • Human susceptibility and mode of transmission is not clear. (B609.2.w2)
    • Resistance is T-lymphocyte dependent so humans with CD4 T-lymphocyte deficiences are reported to be particularly susceptible to microsporidian infections as are patients who are on immunosuppressive drugs. (B602.20.w20)
    • Infections in humans is thought to be mainly through environmental spore contamination, for example, via contaminated water sources. (B601.11.w11)
    • There have been no reports or evidence of direct transmission of this disease from rabbits to humans (B601.11.w11, B614.10.w10) "although infections in humans have been shown to be the same strain that infects rabbits". (B601.11.w11)
    • It has been shown that human strains may be transferred to rabbits. (B601.11.w11)

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Susceptibility / Transmission

General information on Susceptibility / Transmission

The majority of infections are opportunistic in immunocompromised hosts. (B600.16.w16, B601.11.w11, B603.4.w4, B609.2.w2)
Lagomorphs
Susceptibility
  • Sex
    • There is no sex predilection. (B609.2.w2)
  • Age
    • Clinical disease is most likely to occur in the older or immunosuppressed animal. (B609.2.w2)
    • Phacoclastic uveitis is seen in younger animals. (B609.2.w2)
    • Anecdotal reports show that CNS disease is more likely in the older animal. (B609.2.w2)
  • Breed
    • Dwarf breeds are more commonly affected. (B609.2.w2)
    Immunosuppression will predispose the animal to clinical disease. An asymptomatic rabbit with subclinical infection will often exhibit clinical signs after being subjected to one or more of the following events:
    • poor diet (B609.2.w2)
    • stress (B602.20.w20, B609.2.w2)
    • Unsanitary conditions. (B604.5.w5)
    • concurrent disease (B609.2.w2)
    • glucocorticoid or anti tumour chemotherapy. (B602.20.w20, B609.2.w2)
Transmission
  • Ingestion: the spores are shed in urine and are infective by ingestion of contaminated water or food. (B600.16.w16, B601.11.w11, B602.20.w20, B603.4.w4, B604.5.w5, B614.10.w10, J29.5.w1)
  • Inhalation: spores may also be inhaled. (B600.16.w16, B601.11.w11, B602.20.w20, B603.4.w4)
  • Young rabbits may be infected by their dam within the first few days of life. (B600.16.w16)
    • Maternal transfer of immunity appears to occur in newborn rabbits. (B600.16.w16)
      • Maternal antibodies subside when the young rabbit is around four weeks old. (B604.5.w5)
    • The major exchange between the doe and her young occurs between the fourth and sixth weeks of life. Sero-conversion of the young rabbits occurs during the seventh and ninth weeks of life. (B604.5.w5)
  • Transplacental transmission also occurs. (B601.11.w11)
    • Transplacental transmission, with the organism entering the lens during development of the eye in utero is thought to be responsible for cases of ocular encephalitozoonosis. (B600.11.w11, B601.12.w12)
  • Most rabbits are exposed to this disease in utero or at birth. (B609.2.w2)
  • Endo- or ectoparasites may act as transport/vector hosts. (B603.4.w4, B614.10.w10)
  • Rabbits that are showing clinical signs of this disease are no longer shedding spores as the spores are only shed for three weeks after infection. (B609.2.w2)

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Disease has been reported in either the wild or in captivity in:

In Lagomorphs
  • Encephalitozoonosis is an important disease of domestic rabbits. (B614.10.w10)
  • Fatal encephalitozoon encephalomyelitis in a wild, three-week-old cottontail rabbit (Sylvilagus sp.) which had been in captivity for four days. (J4.127.w2)
  • Antibodies were detected in three wild rabbits in Scotland. [1979] (J21.26.w1)
  • In a survey of clinically healthy pet rabbits in North Yorkshire, 6/23 asymptomatic rabbits were seropositive as were 8/12 which were asymptomatic but living with a seropositive rabbit. 38/53 rabbits with neurological signs were seropositive as were all seven rabbits with ocular lesions. (J3.152.w5)
  • In domestic rabbits in the UK, 52% of 97 clinically healthy rabbits from England, Wales and Scotland (samples collected November 2001 - July 2003) were seropositive. (J3.158.w2)
  • A survey of wild Oryctolagus cuniculus - European rabbit from south-western Western Australia detected antibodies (indirect IFA) in 20 of 81 individuals. Encephalitozoon cuniculi was isolated from brain and kidney of five of the seropositive rabbits. In laboratory rabbits, 22/29 were seropositive and the organism was isolated from the urine of one rabbit and from the brain and kidney of eight of the seropositive rabbits. [1995](J24.75.w3)
  • Note:
    • In wild rabbits in England and Scotland, a serological survey (1979) found only two of 175 sera to be weakly reactive and none to have titres of 1:10 or more by indirect immunofluoresecent antibody test. [1980](J21.28.w1)
    • A survey of 823 wild Oryctolagus cuniculus - European rabbit from Victoria, Australia, and 46 hares (Lepus europaeus - Brown hare), as well as 57 rabbits from New Zealand, did not detect any antibodies; wild rabbits were readily infected experimentally. [1980](J19.84.w2).
  • Antibodies detected in 25 - 75% of rabbits in laboratory rabbit colonies in Australia [1975]. (J83.9.w1)
In Bonobos
  • Encephalitozoon cuniculi was detected using PCR in faeces of one of five Pan paniscus - Bonobos tested at Leipzig Zoo, Germany, and two of four bonobos tested at Twycross Zoo, UK, but 0/5 tested at Antwerp Zoo, Belgium. (J119.58.w1)

Further information on Host species has only been incorporated for species groups for which a full Wildpro "Health and Management" module has been completed (i.e. for which a comprehensive literature review has been undertaken). Host species with further information available are listed below:

Host Species List

(List does not contain all other species groups affected by this disease)

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Disease has been specifically reported in Free-ranging populations of:

In Lagomorphs
  • Fatal encephalitozoon encephalomyelitis in a wild, three-week-old cottontail rabbit (Sylvilagus sp.) which had been in captivity for four days. (J4.127.w2)
  • A survey of wild Oryctolagus cuniculus - European rabbit from south-western Western Australia detected antibodies (indirect IFA) in 20 of 81 individuals. Encephalitozoon cuniculi was isolated from brain and kidney of five of the seropositive rabbits. [1995](J24.75.w)
  • Note:
    • In wild rabbits in England and Scotland, a serological survey (1979) found only two of 175 sera to be weakly reactive and none to have titres of 1:10 or more by indirect immunofluoresecent antibody test. (J21.28.w1)
    • A survey of 823 wild Oryctolagus cuniculus - European rabbit from Victoria, Australia, and 46 hares (Lepus europaeus - Brown hare), as well as 57 rabbits from New Zealand, did not detect any antibodies; wild rabbits were readily infected experimentally. [1980](J19.84.w2).

Further information on Host species has only been incorporated for species groups for which a full Wildpro "Health and Management" module has been completed (i.e. for which a comprehensive literature review has been undertaken). Host species with further information available are listed below:

Host Species List

(List does not contain all other species groups affected by this disease)

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Environment/Geography

General Information on Environmental Factors/Events and Seasonality

  • This parasite may remain infective in contaminated bedding and environment.
    • Dry spores: at 22░ C they remain infective outside of the host for over a month. (B602.20.w20, B603.3.w3)
    • Wet spores: may remain infective for 98 days. (B603.3.w3) 

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Regions / Countries where the Infectious Agent or Disease has been recorded

  • Worldwide. (B609.2.w2)

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Regions / Countries where the Infectious Agent or Disease has been recorded in Free-ranging populations

  • Fatal encephalitozoon encephalomyelitis was reported in a wild, three-week-old cottontail rabbit (Sylvilagus sp.) which had been in captivity for four days [reported from Connecticut, USA]. (J4.127.w2)

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General Investigation / Diagnosis

General Information on Investigation / Diagnosis

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Lagomorphs An antemortem definitive diagnosis is a problem because:
  • A positive antibody titre only indicates exposure to the parasite; (B609.2.w2)
  • Rabbits will often respond to treatment minimally or even not at all; (B609.2.w2)
  • Many rabbits will improve without any treatment; (B609.2.w2)
  • Identification of the parasite along with characteristic inflammation in affected tissues is really needed for a definitive diagnosis and this is usually obtained at post mortem examination. (B609.2.w2)
Investigation
  • CBC: usually unremarkable. (B609.2.w2)
  • PCV: may be increased with dehydration possibly secondary to anorexia or renal disease. (B609.2.w2)
  • BUN and creatinine: may be increased with renal disease (rare). (B609.2.w2)
  • Urinary detection of organisms: 
    • Urine is centrifuged then examined for the presence of Encephalitozoon cuniculi; indirect immunofluorescence can be used to detect the organisms. (J83.11.w1)
    • Gram's stain may show the oval spores which are 2.5 x 1.5 Ám in diameter. (B603.4.w4. B609.2.w2)
    • These spores are reportedly only passed for up to three weeks following infection and are not usually present in the urine when neurological, renal or ophthalmological signs are present. (B609.2.w2)
    • However, a study found that the spores were excreted by six weeks after infection and this may last up up to three months. (B602.20.w20, J31.26.w1)
    • PCR may be used to detect the organism in urine. (B603.4.w4, J32.151.w1)
    • Note: organisms are excreted in urine intermittently in chronic infection; in one study they were noted to be found in about a third of urine specimens, with individual variation between rabbits - from shedding in as few as 3/23 samples to shedding in about 50% of samples. (J83.9.w1, J32.151.w1)
  • Serological testing:
    • Tests include carbon immunoassay (CIA), ELISA, and indirect immunofluorescent antibody (IFA). (B602.20.w20, B604.5.w5, B609.2.w2, J83.34.w1)
    • Their usefulness is limited in pet rabbits because a positive antibody titre will only indicate exposure and will not confirm Encephalitozoon cuniculi as the cause of the clinical signs. (B603.4.w4, B609.2.w2)
    • Antibody titres often become positive within two weeks post infection and usually do not continue to increase with active infection nor decline with treatment. (B609.2.w2)
    • A negative titre probably rules out Encephalitozoon cuniculi because clinical disease rarely occurs less than one month post infection. (B603.3.w3)
    • It has been suggested that here is no correlation between antibody titres and severity of disease or shedding of the organism. (B609.2.w2)
      • However, another study found " a significant correlation between high antibody levels and signs of neurologic disease in rabbits" using ELISA. (B602.20.w20)
    • It is not known if exposed rabbits will eventually become seronegative. (B609.2.w2)
    • "Seroconversion precedes renal shedding by 4 weeks so antibody assay tests could be used in a multirabbit household to screen in-contact animals following a clinical case and remove any seropositive animals before they become infective". (B601.11.w11)
    • Serum antibodies may be detectable as early as two weeks before spores are detected in tissues or urine. The antibodies will peak by six weeks after infection. (B602.20.w20)
    • "A presumptive diagnosis is made based on a single high antibody titre, or rising paired antibody titres, in conjunction with clinical signs". (B601.11.w11)
    • Offspring from seropositive dams: these animals have maternal antibody up to four weeks of age and then this diminishes. The animals own antibody titres will then rise by eight to ten weeks of age and peak at around fourteen weeks. (B602.20.w20)
  • Radiographs:
    • Skull- rule out otitis media / interna. (B609.2.w2)
    • Spinal- rule out spinal trauma or disease. (B609.2.w2)
    • Kidneys- may see malformed small kidneys if there is severe renal involvement of this infection. (B609.2.w2)
  • CSF analysis:
    • Inflammatory changes are non specific but suggestive of Encephalitozoon cuniculi. (B603.4.w4)
  • CT or MRI: to rule out CNS neoplasia, bulla disease or CNS abscess. (B609.2.w2)
Presumptive diagnosis
  • This is often based on clinical signs, exclusion of other differential diagnoses, a single positive antibody titre (or rising paired antibody titres (B601.11.w11)) and sometimes response to therapy.

(B601.11.w11, B602.20.w20, B609.2.w2, B614.10.w10, J29.5.w1)

Definitive diagnosis
  • Histopathology: evidence of Encephalitozoon cuniculi organisms and resultant lesions found on histopathologic examination in locations that anatomically correlate with the observed clinical signs.
  • In ocular disease: detection of Encephalitozoon cuniculi organisms in lens material. (J541.3.w1, J541.7.w1)
    • Ovoid Gram-positive organisms (J541.3.w1); confirmed by PCR. (J541.7.w1)

(B601.11.w11, B602.20.w20, B609.2.w2, B614.10.w10, J29.5.w1)

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Similar Diseases (Differential Diagnosis)

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Lagomorphs
For vestibular signs 

For rear limb paresis / ataxia

For intraocular disease (anterior uveitis)

(B609.2.w2)

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Treatment and Control

Specific Medical Treatment

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Lagomorphs Treatment of this disease is not always successful but in many cases it has at least led to an improvement. However, if the patient does not receive any treatment there is increased likelihood of this animal being euthanised due to severe neurologic disease. (B602.20.w20)

The aims of treatment are to reduce inflammation and prevent the formation of spores. (B601.11.w11)

  • Benzimidazole anthelmintics
    • Effective against this parasite in vitro and they have been reported to prevent experimental infection in the rabbit. However, their efficacy in rabbits showing clinical signs of this disease is not known. There are anecdotal reports suggesting a response to treatment but often rabbits with neurological signs may improve with or without treatment. (B609.2.w2)
    • Long term treatment is recommended, as treatment will only prevent replication rather than killing the parasite. (B609.2.w2)
    • Eradication of this parasite is possible with prolonged use of a benzimidazole. (B603.4.w4)
    • Treatments include using one of the following:
      • Fenbendazole
        • 20 mg/kg orally every 24 hours for 28 days. (B601.11.w11, B602.20.w20, B603.4.w4, B609.2.w2)
        • This is presently the only drug with published data showing it to be effective in vivo. It is not effective against clinical disease but in the elimination of the parasite from rabbits infected naturally. It has also been effective in vivo in preventing infection and serological conversion in animals experimentally inoculated with this parasite. (B602.20.w20, B603.3.w3, B603.5.w5)
      • Oxibendazole
        • 30 mg/kg orally every 24 hours for 7 to 14 days then reduce to 15 mg/kg every 24 hours for 30 to 60 days. (B602.20.w20, B609.2.w2)
          • In some cases, the neurological signs have abated during treatment with this drug and then reoccurred after the treatment was stopped. Treatment with oxibendazole should be continued indefinitely in these cases at 15 to 30 mg/kg orally every 24 hours. (B602.20.w20)
      • Albendazole
        • 20-30 mg/kg every 24 hours for 30 days then 15 mg/kg PO every 24 hours for another 30 days. (B602.20.w20, B609.2.w2)
        • 10-15 mg/kg orally every 24 hours for three months. (B602.20.w20)
        • This drug is reportedly the most effective agent for the treatment of microsporidiosis in humans. It is thought to have better absorption from oral administration in comparison to the other benzimidazoles. It has also been reported that dexamethasone administration increases the plasma levels of albendazole by 50 %. (B602.20.w20)
        • Associated with bone marrow toxicity in cats and dogs but the toxicity in rabbits is not known; "however, anecdotal reports of pancytopenia leading to death in rabbits exist".
          (B609.2.w2)
  • Antibiotics
    • Some practitioners prescribe systemic broad spectrum antibiotic therapy to be used concurrently with the 28 day course of fenbendazole. One of the following can be used:
  • Systemic corticosteroids
    • Anti inflammatory medication is most important in acute disease. The clinical signs seen are caused not by the presence of the parasite but by the granulomatous inflammation. (B603.4.w4)
    • Dexamethasone:
      • 0.1 - 0.2 mg/kg subcutaneously every 48 hours for three doses may be used in rabbits that present with the acute stage of disease. (B601.11.w11)
      • "0.1 mg/kg SC q24h, then at 48h for two more doses". (B602.20.w20)
    • Some practitioners advocate this for treating CNS granulomatous inflammation induced by the Encephalitozoon cuniculi infection. Most advise a single immunosuppressive dose of a short acting corticosteroid and then subsequent anti-inflammatory doses if necessary. However, this is controversial. (B609.2.w2)
    • Precautions:
      • The use of either topical or systemic corticosteroids is controversial in rabbits with encephalitozoonosis. Rabbits are particularly sensitive to the immunosuppressive effects of these drugs. It is possible that they may exacerbate the encephalitozoonosis or a subclinical bacterial infection. (B609.2.w2)

For the treatment of phacoclastic uveitis
  • 1% Prednisolone acetate drops every 6 to12 hours for 5 days. (B609.2.w2)
    • See precautions of corticosteroids above.
  • Use benzimidazole anthelmintics concurrently. (B609.2.w2)
  • Albendazole, 30 mg/kg orally every 24 hours for four weeks, plus topical steroids. (B601.11.w11)
    • In one case, the lens and associated granuloma were removed by phacoemulsification. Recurrent granuloma in the anterior chamber was treated successfully with albendazole orally (30 mg/kg daily for four weeks, then 15 mg/kg daily for four weeks) plus topical 1% prednisolone (every six hours for four weeks then every 12 hours for four weeks). (J541.7.w1)

For the treatment of severe vestibular signs (torticollis or rolling) or seizures
One of the following medications can be used:
  • Diazepam
    • 1-2 mg/kg intramuscularly (B609.2.w2)
    • 0.5 mg/kg subcutaneously, intramuscularly, or intravenously. May repeat three times in refractory cases. (B601.11.w11)
    • 0.1 mg/kg by subcutaneous injection as necessary. (B602.20.w20)
  • Midazolam
    • 1-2 mg/kg intramuscularly (B609.2.w2)
    • 0.07-0.22 mg/kg intravenously or intramuscularly. May repeat three times in refractory cases. (B601.11.w11)
    • This drug may also be used by subcutaneous injection. (B602.20.w20)

For the treatment of vestibular signs
  • Meclizine
    • 2 - 12 mg/kg orally every 24 hours may reduce the clinical signs, control nausea, and provide mild sedation. (B609.2.w2)
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General Nursing and Surgical Techniques

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Lagomorphs
Nursing
  • Level of care: many rabbits will improve with supportive care alone and can usually be cared for as an outpatient. However, if the patient has severe disease and cannot maintain adequate hydration or nutrition then it will need to be cared for as an inpatient. (B609.2.w2)
  • Fluids: intravenous or subcutaneous fluids will be necessary if there is dehydration. (B609.2.w2)
    • To encourage oral fluid intake, offer fresh water, wet leafy vegetables or flavour water with vegetable juice. (B609.2.w2)
  • It is very important that the patient continues to eat throughout treatment. Anorexia will often lead to gastrointestinal hypomotility, microflora derangement and overgrowth of pathogenic intestinal bacteria. (B609.2.w2) See:
  • Treatment and Care - Supportive Care and Nursing
  • Food and Feeding for Mammals - Convalescent diets / Nutritional support
  • Precautions: take care to avoid aspiration secondary to an abnormal body posture in patients that have brainstem dysfunction or severe head tilts and vestibular disequilibrium. (B609.2.w2)

Surgical techniques
  • Phacoemulsification has been successful in rabbits with phacoclastic uveitis. (B609.2.w2)
  • Enucleation may be required in some rabbits with glaucoma secondary to Encephalitozoon cuniculi infection. (B609.2.w2)
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Preventative Measures

Vaccination --
Lagomorphs --
Prophylactic Treatment

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Lagomorphs
  • In commercial colonies, fenbendazole can be used prophylactically in the feed to decrease the incidence of infection. (B601.11.w11, B602.20.w20)
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Environmental and Population Control Measures

General Environment Changes, Cleaning and Disinfection --

Lagomorphs

  • Good sanitation. (J29.5.w1)
  • Clean the environment daily, because spores are inactivated by most of the common disinfectants including:
    • quaternary ammonium compounds
    • amphoteric surfactants
    • phenolic derivatives
    • alcohols
    • iodophors
    • hydrogen peroxide
    (B609.2.w2, B614.10.w10)
  • Spores are also easily destroyed by autoclaving and boiling. (B601.11.w11)
  • To reduce the risk of urinary transmission, use raised food dishes and use water bottles rather than bowls. (B601.11.w11)
  • Avoid contact with wild rabbits and rodents who could possibly act as a source of infection. (B601.11.w11, B602.20.w20)
Population Control Measures --
Lagomorphs
Establishing an encephalitozoonosis-free breeding colony
  • Ideal method but requires time and expense:
  • House healthy seronegative young rabbits in complete isolation from the other rabbits and in separate cages.
  • Test serum antibody levels every two weeks for two months and then remove any seropositive animals no matter how low the titre.
  • Continue to test until all the animals are negative for one month.
  • Use these animals to set up the breeding colony but continue to test on a monthly basis to provide confirmation of the disease-free status.
  • If the above is not practically feasible, the incidence of infection may be reduced by:
  • Prophylactic use of fenbendazole in feed.
  • Testing and isolation of any positive animals.
  • Good hygiene with disinfection practices used routinely.
  • Using raised food dishes.
  • Using water bottles rather than bowls will reduce the urinary transmission risk.
  • Avoid contact with wild rabbits and rodents who could possibly act as a source of infection.

(B601.11.w11)

Isolation, Quarantine and Screening --
Lagomorphs
Serological testing
  • Ideally, rabbits that are to be used for breeding should be serologically negative. (B609.2.w2)
  • Prior to purchase / introduction to a colony: 
    • Some veterinarians advise serologically testing new rabbits prior to purchase or addition to the colony and excluding those which are seropositive.
      • Antibody titres often develop within two weeks of infection. However, infected rabbits are reported to only shed spores for three weeks following infection. After this three week period, rabbits with subclinical or chronic disease are reportedly not contagious. (B609.2.w2)
      • There has been no correlation shown between antibody titres, clinical signs or shedding of spores. (B609.2.w2)
      • Antibody titres may be useful in developing specific pathogen free colonies. (B609.2.w2)
    • Laboratory rabbits - rigorous testing of all incoming stock is carried out to keep the colony free from this parasite. Any rabbits that are serologically positive are rejected. (B603.4.w4)
  • Routine monitoring: periodic serological testing should be used in monitoring colonies. (B614.10.w10)
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