OVINE HAEMOPHILUS-SOMNUS - EXPERIMENTAL INTRACISTERNAL INFECTION AND ANTIGENIC COMPARISON WITH BOVINE HAEMOPHILUS-SOMNUS

Experimental infection was produced by two of four isolates of ovine H aemophilus somnus given by intracisternal inoculation into two to thre e-month-old lambs. Isolate 2041 (originally obtained from a septicemic lamb in Alberta) caused lethal infection in eight of nine lambs, isol ate 67p from the prepuce of a normal lamb produced less acute disease in four of nine lambs, and the other two isolates (93p and 1190) cause d no detectable disease. Significant lesions were limited to the brain and spinal cord. Purulent meningitis was characteristic but vasculiti s or septicemia were not detected, perhaps due to the route of inocula tion. Since a difference in virulence was noted among strains, we anal yzed surface proteins thought to be virulence factors of bovine H. som nus. Protein profiles of bovine and ovine H. somnus done by sodium dod ecyl sulphate-polyacrylamide gel eletrophoresis showed similar pattern s for virulent bovine isolates and ovine septicemic isolates. Preputia l isolates showed a lower molecular mass major outer membrane protein than septicemic isolates. Antigenic analysis revealed that outer membr ane proteins p270, p78, p76, p40, and p39 were detected in both ovine and bovine isolates except for 1190, which was probably not a true H. somnus isolate. Thus the preputial and septicemic isolates of ovine H. somnus were similar to bovine H. somnus in pathogenicity and in surfa ce antigens.