Investigation of Respiratory Syncytial Virus (RSV) andParainfluenza-3 (PI-3) virus by histopathological and immunohistochemical Methods in sheep and goats ABSTRACT Respiratory Syncytial Virus (RSV) and Parainfluenza type 3 (PI3) virus cause serious respiratory system infections in sheep and goats. It was aimed to investigate the localization and distribution of sheep and goat RSV and PI-3 in lung tissue by histopathological and immunohistochemical methods. The study material consisted of 30 sheep and 24 goat lung paraffin blocks from Samsun and its surrounding regions, which came to Samsun Control and Veterinary Research Institute between 2016-2019. Histopathological changes characterized by bronchial and bronchiolar epithelial degeneration and desquamation, interalveolar septal thickness, epithelialization of the alveolar epithelial surface and inflammatory cells in the alveolar lumen. In addition, hyperplasia of peribronchial lymphoid tissue, hyaline membrane formation and syncytial cells in alveoli were observed less frequently. Althought, bronchiolitis obliterans were not detected in any of the cases. In immunohistochemical staining, RSV antigen was detected in 50% of sheep and 54% of goats, and PI-3 antigen was detected in 40% of sheep and 50% of goats. RSV and PI-3 antigenic distribution of sheep and goats in bronchial and bronchiolar epithelium and cells debris and interalveolar septum were statistically similar (p>0.05). PI-3 antigen in goats was detected more intensely than sheep (p<0.05) in alveolar macrophages statistically. It was concluded that the localization of RSV and PI-3 antigens in sheep and goat lung tissue was detected similar by this study. In addition, it was determined that RSV and PI-3 antigens were common in sheep and goats and it was thought that vaccination should be done for protection.