Encephalitozoonosis (E. cuniculi) in Rabbits

E cuniculi or Encephalitozoon cuniculi is a one-celled organism called a microsporidium. Rabbits can either become infected while they develop within their mother's uterus or by either ingesting or inhaling spores  passed in the urine from rabbits already carrying the disease. Ingested spores pass through the walls of the intestine into the blood where they then travel to other areas of the body. In some rabbits,the disease spreads onward to the kidneys, eye and brain.  Most rabbits show no signs of disease early on in the infection. In some rabbits the disease progressing and can have serious consequences including death if their immune system fils to contain it.  Infection that takes place in the brain results in head tilt and may cause other signs such as weakness, paralysis, blindness, altered appetite, tremors or seizures. It can also cause long term damage to the kidneys resulting in renal insufficiency and failure later in life. In the eye E. cuniculi causes  cataracts and a condition called phacoclastic uveitis. 
A blood test exists to determine if a rabbit has antibodies to E. cuniculi. However, this will only give a veterinarian so much information. It will only tell the doctor if the patient has been exposed to E. cuniculi, it will not tell them if the rabbit has an active infection. Very high titers and an increase in a protein in the blood called an acute phase protein may suggest that an ongoing infection is occuring.
There is no know cure for E. cuniculi, however, long term treatment with an anti-parasitic medication called Fenbendazole will very often control the parasites and treat the symptoms. Most rabbits will be on this medication for life. Rabbit positive for this disease should be kept away from rabbits who are negative or who have no history of exposure to this disease.