Encephalitozoon cuniculi

Encephalitozoon cuniculi is a protozoan 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. 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.

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. There are numerous instances where an E. cuniculi-positive rabbit has lived with an E. cuniculi-negative rabbit without infecting the latter.

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

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.

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. 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.

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.
 * 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 active protozoa. However, note that albendazole has been associated with fatal bone marrow toxicity in rabbits. Ponazuril has also been anecdotally used for up to 30 days, but the safety and efficacy are unknown.

Rabbits with eye inflammation may be prescribed drugs such as fluriprofen ophthalmic solution and oral meloxicam up to 5 days. 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.

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

The following are some links about treatments for E. cuniculi:
 * Esther van Praag. (2011). Various treatment options for Encephalitozoon cuniculi, a protozoal parasite of the nervous system in rabbits?
 * Kathy Smith. (2004). E. cuniculi Treatment Success Stories
 * C Suter et al. (2001). Prevention and treatment of Encephalitozoon cuniculi infection in rabbits with fenbendazole
 * Jennie Langdon. (2002). Calculating Oxibendazole Dosage
 * FF Franssen et al. (1995). Susceptibility of Encephalitozoon cuniculi to several drugs in vitro.
 * Molly Varga. (2015). The truth about E. cuniculi - Virtual Pet Congress 2015 webinar