EXPERIMENTAL REPRODUCTION OF HAEMOPHILUS-PARASUIS INFECTION IN SWINE - CLINICAL, BACTERIOLOGICAL, AND MORPHOLOGIC FINDINGS

Haemophilus parasuis is a common cause of polyserositis and polyarthri tis in swine. Little is known about the mucosal and systemic sites of replication and lesions which follow an aerosol exposure to H. parasui s. In this experiment 5-week-old cesarean-derived, colostrum-deprived (CDCD) pigs were inoculated intranasally with an inoculum containing 2 x 10(9) colony-forming units of H. parasuis. Two principals and one c ontrol pig were necropsied at 12, 36, 84, and 108 hours postinoculatio n (PI) and samples obtained for bacteriologic culture and microscopic examination. Inoculated pigs developed clinical signs of inappetence, reluctance to move, lameness, and a serous nasal discharge. Macroscopi c findings included a fibrinous polyserositis and polyarthritis 36 hou rs PI which became progressively more severe at 84 and 108 hours PI. N o lung lesions were grossly visible; Microscopic lesions included a mi ld purulent rhinitis at each post inoculation interval and fibrinous t o fibrinopurulent synovitis and serositis at 36, 84, and 108 hours PI. A focal suppurative bronchopneumonia was observed in one pig examined at 36 hours PI. The nasal cavity and trachea were the only mucosal si tes from which H. parasuis was reisolated. Haemophilus parasuis was is olated from the blood and systemic sites at 36, 84, and 108 hours PI. Findings presented indicate that intranasal inoculation of 5-week-old CDCD pigs with H. parasuis results in clinical signs and lesions of po lyserositis and polyarthritis typical of held cases and is a useful mo del for the study of H. parasuis pathogenesis. The results also sugges t that H. parasuis initially colonizes the nasal mucosa.