Interaction of Haemophilus parasuis with nasal and tracheal mucosa following intranasal inoculation of cesarean derived colostrum deprived (CDCD) swine.

Twenty-three cesarean derived, colostrum deprived pigs were obtained at 5 wk of age and inoculated intranasally with either 1.4 x 10(8) colony forming units of Haemophilus parasuis or sterile phosphate buffered saline. Pigs were euthanized at 4, 8, 12, 18, 26, or 36 h post-inoculation and tissues from the oropharynx and respiratory tract were obtained for qualitative bacterial culture, immunohistochemistry for H. parasuis antigens, and light and transmission electron microscopy. Haemophilus parasuis was consistently isolated from the nasal cavity (17/17, 100%) and trachea (13/17, 76%) and rarely isolated from the lung (3/17, 18%) and blood stream (1/17, 6%) of infected pigs. Antigens of H. parasuis were sporadically detected on the nasal mucosa (6/17, 35%) and trachea (8/17, 47%). Light microscopic lesions included submucosal and intraepithelial infiltrates of neutrophils and infrequent, patchy loss of cilia. Ultrastructural changes in nasal mucosal epithelial cells included cell protrusion, loss of cilia, and dilation of the cytocavitary network. Bacteria were infrequently identified and were either within an amorphous material at the apical surface of the cilia or were between individual cilia. These results suggest H. parasuis associates with the nasal mucosa and can induce a suppurative rhinitis with nasal mucosal epithelial cell degeneration. This process may represent an initial event in the pathogenesis of H. parasuis infection of swine.

Experimental reproduction of Haemophilus parasuis infection in swine: clinical, bacteriological, and morphologic findings.

Haemophilus parasuis is a common cause of polyserositis and polyarthritis in swine. Little is known about the mucosal and systemic sites of replication and lesions which follow an aerosol exposure to H. parasuis. 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 control pig were necropsied at 12, 36, 84, and 108 hours postinoculation (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. Macroscopic findings included a fibrinous polyserositis and polyarthritis 36 hours PI which became progressively more severe at 84 and 108 hours PI. No lung lesions were grossly visible. Microscopic lesions included a mild purulent rhinitis at each post inoculation interval and fibrinous to 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 sites from which H. parasuis was reisolated. Haemophilus parasuis was isolated from the blood and systemic sites at 36, 84, and 108 hours PI. Findings presented indicated that intranasal inoculation of 5-week-old CDCD pigs with H. parasuis results in clinical signs and lesions of polyserositis and polyarthritis typical of field cases and is a useful model for the study of H. parasuis pathogenesis. The results also suggest that H. parasuis initially colonizes the nasal mucosa.