PATHOGENICITY AND IMMUNOGENICITY OF DIFFERENT ISOLATES OF TELADORSAGIA-CIRCUMCINCTA

The effects on liveweight gain and development of immunity were studie d in lambs trickle infected for 8 weeks with either a benzimidazole-re sistant isolate (Moredun ovine resistant isolate, MORI), a multiple be nzimidazole + ivermectin-resistant isolate (Moredun caprine resistant isolate, MCRI) or an unselected susceptible isolate (Moredun ovine sus ceptible isolate, MOSI) of Teladorsagia circumcincta. Plasma pepsinoge n concentrations of infected groups were significantly elevated compar ed to an uninfected control group (P < 0.001) by day 14. The liveweigh t gains varied markedly but there were no statistical differences betw een the infected and uninfected control groups at any point in time du ring the study. Lambs infected with the MORI had significantly lower f aecal consistency scores than the other challenged groups on days 7 an d 14 (P < 0.05) but from day 21 onwards, faecal consistencies were sim ilar in all of the groups. There was a notable difference in the pre-p atent periods of the different isolates with the MOSI producing positi ve faecal egg counts (FECs) by day 14 of the study. The FECs remained reasonably low once infections had reached patency and there were no f urther differences between the groups. Following administration of ant helmintic to remove residual worms from the trickle infection, no diff erences between the infected groups in terms of worm burden or mucosal mast cell numbers were evident as a consequence of a single challenge infection. The changes in genetic code associated with enhanced resis tance against anthelmintics do not appear to have resulted in any fund amental alteration of the pathogenicity and immunogenicity of these th ree isolates of Teladorsagia. (C) 1998 Elsevier Science B.V.