Rabies in horses: 21 cases (1970-1990)

Abstract

Summary The records of 21 horses with rabies were reviewed. Results of fluorescent antibody testing for rabies antigen in brain tissue were positive in each case. According to the histories, 5 of the horses had been vaccinated for rabies between 4 to 24 months prior to the onset of the clinical signs. Bite wounds were not observed on any of the horses, and exposure to a suspected rabid animal was witnessed in only 5 cases. Clinical signs of disease at the time of initial examination included ataxia and paresis of the hindquarters (9/21, 43%), lameness (5/21, 24%), recumbency (3/21, 14%), pharyngeal paralysis (2/21, 10%), and colic (2/21, 10%). The major clinical signs observed over the course of hospitalization included recumbency (21/21; 100%), hyperesthesia (17/21; 81%), loss of tail and anal sphincter tone (12/21; 57%), fever (11/21; 52%), and ataxia and paresis of the hindquarters (11/21; 52%). Mean survival time after the onset of clinical signs was 4.47 days (range, 1 to 7 days). Supportive treatment, given to 9 horses, had no effect on survival time and did not correlate with the detection of negri bodies at necropsy. Cerebrospinal fluid (csf) was obtained from 6 horses and was determined to be abnormal in 5. The most common abnormality was a slightly high total cell count (5/6), with a predominance of lymphocytes (4/6). The csf total protein concentration was high in only 2 horses. At necropsy, there was gross evidence of diffuse brain edema, meningeal congestion, and focal areas of hemorrhage in 5 horses (24%). The major histologic findings included diffuse perivascular cuffing with leukocytes (predominantly lymphocytes) in the meninges and neural parenchyma (14/21; 67%), neuronal degeneration and neuronaphagia (11/21; 52%), gliosis (9/21; 43%), and malacia of the gray matter of the spinal cord (6/21; 28%). Negri bodies were not identified in brain tissue of 11 horses (53%). Horses that survived 4 or more days after the onset of clinical signs were significantly (P < 0.025) more likely to have negri bodies in the neural tissues.