Rabies is a viral disease transmitted in the saliva of infected animals. Once in the brain, it causes a variety of symptoms in various species. If the rabies virus reaches the brain, it is fatal.
Some animals just look ill, and some develop vague, weird neurologic signs.
The horse was just non-specifically stiff behind, positive to flexion of both hocks, and had been examined by several other very competent veterinarians. None of us really came up with anything, except by the time I saw it, it did have just a little eyelid droop. The horse subsequently died of rabies without showing any more dramatic symptoms. The number of reported cases of rabies has doubled in the last year. The animal vaccine is relatively cheap, and should be performed by a veterinarian so that there is an official medical record documenting the animals vaccination status.