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Encephalitozoon cuniculi

Encephalitozoon cuniculi is a microsporidian parasite that various studies suggest up to 80% of the healthy rabbit population carries without ever showing clinical symptoms or development of the disease encephalitozoonosis.[1][2] The parasite is also often referred to as E. cuniculi or EC. It is mostly an opportunistic infection in immunocompromised hosts including rabbits, mice, guinea pigs, hamsters, dogs, cats, primates, and humans.[1] While microsporidia were originally thought to be a (primitive) protozoa, they are no longer labeled as such. The proper taxonomic position of this group is still under revision, but is understood to be related to fungi in some manner, though that relation remains unclear.[3]

USDA APHIS. (2023). Encephalitozoon Cuniculi in Rabbits – Small Pet Welfare Symposium September 2023

Causes

Not much is known about the parasite, but the main path of transmission appears to be from a mother to her litter rather than through infected droppings and urine.[2] There are numerous instances where an E. cuniculi-positive rabbit has lived with an E. cuniculi-negative rabbit without infecting the latter.[2]

Rabbits can be pre-disposed to an active infection due to stress, poor diet, concurrent disease, or chemotherapy.[1]

Symptoms

E. cuniculi infections can effect the kidney, eyes, and central nervous system. Most animals are asymptomatic, and the true incidence of clinical disease is unknown.[1]

Active symptoms can include the following:

  • Sensitivity to light (photophobia)
  • Development of excess white blood cells in the eye (hypopyon)
  • Inflammation in the eye
  • Cataracts
  • Head tilt, rolling, involuntary eye movement (nystagmus)
  • Seizures and tremors
  • Paresis/paralysis or stiff rear limb gait
  • Incontinence
  • Non specific signs of kidney failure such as lethargy, depression, anorexia, and weight loss.

Diagnosis

Diagnosis of an E. cuniculi infection is usually presumed based on clinical signs, the exclusion of other possible diagnoses, positive antibody titers, and response to treatment. A definitive diagnosis is difficult since a positive antibody titer indicates exposure only, and rabbits often respond minimally or not at all to treatment or may commonly improve with no treatment at all.[1] A postmortem examination is required to identify the organisms in affected tissues.

Gram staining on urine can show E. cuniculi spores, but they are only passed for up to 3 weeks following infection, and are generally not present in urine if other physical signs are present.[1]

Treatment

Treatment is usually mostly supportive care and includes the following:

  • Restrict or confine rabbits with neurological signs by providing padded cages for rabbits with severe head tilt.
  • Encourage normal activity as it may speed up the recovery of normal balance.
  • Make sure that the rabbit continues to eat by offering a variety of fresh vegetables or syringe-feeding a support food like Critical Care as necessary. Do no offer any high-carbohydrate or high-fat nutritional supplements.[1]
  • Encourage water intake by offering fresh water, wetting vegetables, or flavoring water with rabbit-safe juices.

Benzimidazole drugs such as fenbendazole, oxibendazole, or albendazole are often prescribed for 30 to 60 days for rabbits with a suspected E. cuniculi infection to attempt to kill any actively replicating spores.[1] Treatment will only prevent replication of the organism, not actually eliminate it. However, note that benzimidazoles has been associated with fatal bone marrow toxicity in rabbits, most commonly at the 30-day mark, but also at the 14-day mark.[4][5][6] It is prudent to evaluate bloodwork before treatment has started in addition to 7-10 days into therapy to rule out any signs of bone marrow suppression, which can be reversed if therapy is stopped immediately.

Some negative experiences with benzimidazole drugs during treatment:

Ponazuril has also been anecdotally used for up to 30 days, but the safety and efficacy are unknown.[1]

Rabbits with eye inflammation may be prescribed drugs such as fluriprofen ophthalmic solution and oral meloxicam up to 5 days.[1] Topical and systemic corticosteroids to decrease any eye inflammation and disease development is controversial as rabbits are very sensitive the to the immunosuppressive effects, and it may exacerbate signs of infection.[1]

Rabbits with head tilt or seizures can be prescribed diazepam or midazolam, and meclizine.[1]

The following are some links about treatment options for E. cuniculi:

Experiences

Further reading

See also

References

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Oglesbee, B. (2011). Blackwell's five-minute veterinary consult: Small mammal. (2nd ed.).
  2. ↑ 2.0 2.1 2.2 Medirabbit.com. (n.d). Various treatment options for Encephalitozoon cuniculi, a protozoal parasite of the nervous system in rabbits ? Retrieved 27 Dec 2018 from http://www.medirabbit.com/EN/Neurology/cuniculi/pyrimethamine.htm
  3. ↑ CDC.gov. (n.d). DPDx - Laboratory Identification of Parasites of Public Health Concern - Microsporidiosis. Retrieved 18 May 2024 from https://www.cdc.gov/dpdx/microsporidiosis/index.html
  4. ↑ Jennifer Graham, DVM, Dipl ABVP, et al. (2014). Benzimidazole toxicity in rabbits. Retrieved 27 Feb 2023 from https://www.researchgate.net/publication/260591209_Benzimidazole_toxicity_in_rabbits
  5. ↑ Jennifer E. Graham DVM, Dip. ABVP. (2014). Benzimidazole Toxicosis in Rabbits: 13 Cases (2003 to 2011). Retrieved 27 Feb 2023 from https://www.sciencedirect.com/science/article/abs/pii/S1557506314000469
  6. ↑ Jennifer Graham DVM, Dipl ABVP, et al. (2022). Encephalitozoon cuniculi – Biology, Diagnostics, and Treatment – Q&A. Retrieved 08 Feb 2024 from https://www.pure.ed.ac.uk/ws/portalfiles/portal/360163648/ECUNICULI_masterclass_AEMV_Final_submission.pdf
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