E. cuniculi is caused by a protozoa – a single-celled organism –with the full name Encephalitozoon cuniculi. Affecting the nervous system and the kidneys, E. cuniculi is spread between rabbits via urine, or during pregnancy. In kits infected while still in the uterus, eye signs may develop as they reach early adulthood. A hardy parasite, E. cuniculi can survive for long periods in the environment, although infection from bunny’s mother is the most common route of infection.
The most frustrating aspect of E. cuniculi is its unpredictability. More than half of all rabbits have antibodies to E. cuniculi, meaning at some point in their lives they have been exposed to the E. cuniculi parasite. Thankfully, the actual numbers of rabbits who suffer with signs of E. cuniculi infection are much lower than this, but this means it can be incredibly difficult to prevent rabbits being exposed, or to predict which rabbits will show signs of infection.