Heads of 100 Awassi sheep were examined for etiology of frontal sinusitis and rhinitis in Jordan. Both affections associated significantly (p < 0.05) and were diagnosed in 65% and 90%, respectively and were found to be significantly different (p< 0.05) among the examined age-groups. A total of 58 (58%) bacterial strains were diagnosed as members of Pasteurella/Mannheimia (P/M). Of those, 27 isolates were purely isolated. Besides, the L₂ and/or L_3, O. ovis larval stages were collected from 56 (56%) heads. Sinusitis and rhinitis affections associated significantly (p< 0.05) with the number of collected living, unlike the dead, L2 instars.

The M. haemolytica, M. trihalosi and P. multocida, were identified in 50%, 36.2% and 13.8%, respectively. All of the Pasteurella/Mannheimia isolates were lethal to Swiss Albino mouse and produced the siderophore while 28 (48%) of them could agglutinate the sheep RBCs.

The larvicidal effect of Pasteurella/Mannheimia isolates was examined on L2 O. ovis larval stage. The highest effect was demonstrated within 24 hours. The three identified Pasteurella/Mannheimia species revealed a larvicidal effect fluctuated between 62% and 64% while their mouse lethality fluctuated between 67% and 88%. Sheep frontal sinusitis and rhinitis were concluded to be highly prevalent in Awassi sheep in Jordan especially among the elder animals with remarkable association between Pasteurella/Mannheimiaspp. and O. ovis causative agents. Further study on the larvicidal effect of Pasteurella is invited.