Mucosal inflammatory responses after experimental infection with gastrointestinal nematodes in resistant and susceptible sheep naturally infected with Oestrus ovis

Recent epidemiological observations from field studies indicated that sheep selected for resistance to digestive nematodes were more infected than sus ceptible ones with the nasal bot fly, Oestrus ovis. The present study was u ndertaken to verify these informations and to explore the possible associat ed mechanisms. After a whole grazing season and an anthelmintic drench, two groups of 6 rams belonging respectively to 2 flocks with different resista nce status to parasitic nematodes were experimentally infected with a mixtu re of Haemonchus contortus, Trichostrongylus colubriformis and Teladorsagia circumcincta infective larvae. The worm populations in the gastrointestina l tract, the Oestrus ovis populations in the nasal cavities and the intensi ty of inflammatory reactions (number of mast cells, eosinophils and globule leucocytes) in the respiratory and digestive mucosae were compared in the 2 groups. No differences were found in the worm numbers and in the cell pop ulations in the digestive tract and this lack of difference was due to acqu isition of immunity to nematodes in both lines of rams at the end of the gr azing season. In contrast, the mean number of O. ovis larvae was higher in the resistant group compared to the susceptible one (6.3 vs 2.8) and the nu mber of eosinophils was significantly higher in the septum and ethmoid in t his resistant group. These results tend to confirm the higher susceptibilit y to O. ovis in animals selected for resistance to digestive nematodes. The y also suggest that the intensity of inflammation in the nasal mucosae migh t be positively related to the intensity of infection with O. ovis.