loss of muscle control

Question
Dear Doctor,

I have two outdoor bunnies.  we believe them to be siblings, one male, one female, and about 3 years old.  yesterday evening i discovered the female was having some sort of motor problem.  she very clumsily ran from me and fell over backwards trying to scramble down her pen chute.  in the house, i put her on the floor to observer her motion.  she really didn't even want to move.  she wobbled alot, and if she did turn to look at something, her front feet would stay planted and only with great effort would she  place them in front of her.  first thing this AM she went to the vet, who over the course of a day did X-rays and blood tests, only to find nothing.  she is prescribing 1.5ml twice/day of Baytril, and .2ml once/day of Metacam.  the bunny doesn't appear to be in pain at all; still has an interest in food, and is thirsty.  last night there was also a twitchy spasming in her shoulders when she would try to move.  it was subtle and would only jerk 2 or 3 times.  today, she cannot do anything.  we took her outside where she became excited and literally dragged herself in an arc, face down in the grass.  she can hardly hold her head up, and on occasion she would twist it high.  and then, just this evening, the male sibling has begun exhibiting the same symptoms, he is wobbly, particularly in his hind legs although when running, he appeared to be very weak in his front legs, his chin just skimming the grass when running (these are 8 lb. rabbits).  to boot, i have an indoor bunny that just last week, we brought outside to graze the grass, and she visited all the same spots the other two favor.  now i fear for her.

i have confidence in my vet, she is a bunny vet,but she is stumped.  i probably could have noticed this sooner.  do you think we are on the right track?  is there anything else we should consider?  thank you so much for your help.  

Answer
Dear Tiffany,

Wow, this is scary.

I can think of a few things to consider:

1.  If there are wild raccoons or skunks in the area where you live, this could be something horrific known as Baylisascaris procyoni (or a different species from a skunk).  This nematode parasite is normally an intestinal inhabitant of raccoons and skunks, but if the wrong intermediate host ingests it, the larvae can migrate into the central nervous system and cause terrible neurological damage.  There is no treatment of which I am aware.

2.  Have pesticides or fertilizers been used on the lawn?  The vet could take a blood sample to check for signs of toxicity reaction in the blood.

3.  If  you have ticks in your area, consider the very real possibility of Lyme disease.  This can be treated with specific antibiotics, but is very hard to diagnose.  If there is the least suspicion that this could be the problem, you might ask the vet about treating, just in case.

4.  I doubt this is the problem, with such acute onset, but there's always the possibility of Encephalitozoon cuniculi.  Please see:

www.bio.miami.edu/hare/paresis.html

5.  I'm guessing that you're aware that heat is extremely dangerous to rabbits.  Heat stroke claims many rabbit lives this time of year.  If rabbits overheat, they can exhibit neurological symptoms like this, but they tend to resolve when the rabbit's body returns to its normal temperature.

The fact that both bunnies are showing symptoms suggests that something in the environment is to blame.  But finding what it is might be tricky.  I hope some of these suggestions will help a little "light bulb" go off.

Good luck, and please keep me posted if you have time.
Dana