Dr. Hailu, YakobMeseret, Melke2018-06-292023-11-302018-06-292023-11-302015-10http://etd.aau.edu.et/handle/123456789/4923A cross sectional study was undertaken in three purposively selected horse-breeding districts of the Arsi–Bale highlands of Ethiopia, namely Dodola, Assassa and Adaba from March 2015 to the end of June 2015. The aim of this study was to describe the neurologic signs and the pathologic findings in the nervous system of horses naturally affected by dourine; and to reveal the presence of the parasite in the nervous tissue or cerebrospinal fluid or in both. For this purpose, a total of 20 local breed of horses with naturally occurring neurologic signs of dourine were considered as study animals. Out of the 20 animals, 12 horses were clinically positive and then selected. From jugular vein of each animal, 7.5 ml and 10 ml of blood using heparinised and plain vacutainer tubes were collected for parasitological (Woo) test and serological (CATT) tests, respectively. The most common signs in the horses were notable weight loss, depigmentation on the vulva and perineal region, and hind legs paralysis. Out of the 12 horses, 2 mares revealed strong seropositive result in CATT test and were subjected for post mortem examination and followed by histopathological analysis. There were no clear gross pathological lesions in the brain, spinal cord and sciatic nerves of the two mares. None of the animals examined showed trypanosomes in Giemsa-stain as well as in blood samples by Woo test. Histopathological examinations of nervous tissue (cerebral cortex, cerebellum, spinal cord and sciatic nerve) showed lesions primarily on the lumbar and sacral regions of the spinal cord and the left sciatic nerve. The primary lesions were degenerative changes and neuronal necrosis of the spinal cord, as well as cellular infiltration and degeneration of the sciatic nerves. Therefore, the present study disclosed that clinically sick horses being seropositive without parasites in the blood as well as nervous tissues revealed moderate degree of pathological lesions. Further sensitive and specific diagnostic techniques need to be applied in order to detect parasitaemia. On the other hand immunological methods seem vital to determine the exact cause of the lesion. Key words: Arsi–Bale highlands, CATT, Dourine, Ethiopia, Histopathology, Horses, Woo testenArsi–Bale highlandsCATTDourineEthiopiaHistopathologyHorsesWoo testThesis