CLINICOPATHOLOGICAL VARIATION IN RACCOONS INFECTED WITH DIFFERENT STREET RABIES VIRUS ISOLATES

Ten raccoons were divided into two random groups (groups 1 and 2) of f ive animals each. Group 1 raccoons were inoculated intramuscularly in the masseter muscle with a raccoon rabies virus isolate obtained from a natural case of raccoon rabies from the northeastern USA, Group 2 ra ccoons were infected by a similar route with a Latin American canine i solate of rabies virus. Raccoons either died suddenly or developed neu rologic signs compatible with rabies. Clinical signs of rabies in grou p 1 raccoons were more severe than in group 2. Raccoons in group 1 eit her died acutely or were euthanized within 25 days ((x) over bar +/- S D = 20.6 +/- 2.7 days) postinfection, whereas all group 2 raccoons sho wed neurologic signs and were euthanized within 17 days (14.2 +/- 2.2 days) postinfection. Light microscopic findings revealed extensive non suppurative encephalitis predominantly located in the cerebrum and bra in stem of raccoons in group 1, whereas in group 2 raccoons the lesion s were confined to the brain stem regions. In group 1 raccoons, Negri bodies were commonly seen on hematoxylin and eosin (HE)-stained sectio ns of brain and in ganglion cells of 5 other tissues (trigeminal nerve , salivary glands, duodenum, pancreas, adrenal gland). Negri bodies, h owever, were either absent or were only occasionally observed in corre sponding tissues of raccoons infected with the canine strain (group 2) . Paraffin-embedded tissue sections were also examined for Negri bodie s by an immunoperoxidase test, which revealed results similar to the H E findings. Results of this study are compared with histopathologic an d immunohistochemical findings in raccoons naturally infected with rab ies.