sudden death of 4month old bunny

Question
Our bunny, Clover, suddenly became unable to move her hind legs then paralysis quickly spread until she couldn't even hold her head up and eventually she couldn't even open her mouth.  We took her to the vet saturday when the initial hind paralysis began. He x-rayed her, no signs of trauma.  Gave her some meds for parasites but she passed away the next morning.
We are devastated.  What could have been wrong with what appeared to be and extremely healthy bunny until three days ago?  Thankyou for your help.

Answer
Dear Lisa,

I am very sorry about the loss of your friend.

Per-acute onset of signs of Encephalitozoon cuniculi is rare, but not impossible.  Usually, though, there is far more time involved between the onset of parlysis and illness, and the parasite is not often acutely deadly.  

Unfortunately, only a necropsy with histopathology of major organs would reveal the most likely cause of death.  There's not much to go on here.  Was she ever outdoors where wild raccoons or skunks leave waste?  A nematode parasite, Baylisascaris, can cause devastating neurological signs, though it is also usually not so quick to kill.

Did anyone take her temperature?  A systemic infection might cause the signs you describe, and must be treated immediately and aggressively if the bunny is to be saved.  Bloodwork might also have helped reveal what was going on--but unfortunately, it is too late for that.

I am very sorry, and wish I could give you a certain answer.  But in cases like this, it is just not possible to know.  

I am sending many healing thoughts at this very sad time.

Dana