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Pathogenicity and immunogenicity of different isolates of Teladorsagia circumcincta
M Barrett1, F Jackson, J F Huntley
1Moredun Research Institute, Edinburgh, UK.
Abstract:
The effects on liveweight gain and development of immunity were studied in lambs trickle infected for 8 weeks with either a benzimidazole-resistant isolate (Moredun ovine resistant isolate, MORI), a multiple benzimidazole + ivermectin-resistant isolate (Moredun caprine resistant isolate, MCRI) or an unselected susceptible isolate (Moredun ovine susceptible isolate, MOSI) of Teladorsagia circumcincta. Plasma pepsinogen concentrations of infected groups were significantly elevated compared to an uninfected control group (P < 0.001) by day 14. The liveweight gains varied markedly but there were no statistical differences between the infected and uninfected control groups at any point in time during the study. Lambs infected with the MORI had significantly lower faecal consistency scores than the other challenged groups on days 7 and 14 (P < 0.05) but from day 21 onwards, faecal consistencies were similar in all of the groups. There was a notable difference in the pre-patent periods of the different isolates with the MOSI producing positive faecal egg counts (FECs) by day 14 of the study. The FECs remained reasonably low once infections had reached patency and there were no further differences between the groups. Following administration of anthelmintic to remove residual worms from the trickle infection, no differences 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 resistance against anthelmintics do not appear to have resulted in any fundamental alteration of the pathogenicity and immunogenicity of these three isolates of Teladorsagia.
Insights
Anthelmintic resistance in Teladorsagia circumcincta did not alter parasite pathogenicity or immunogenicity in lambs. Genetic changes conferring resistance did not impact liveweight gain or immune responses to infection.
Area of Science:
- Veterinary Parasitology
- Sheep Health
- Anthelmintic Resistance
Background:
- Teladorsagia circumcincta is a significant gastrointestinal nematode in sheep.
- Anthelmintic resistance, particularly to benzimidazoles and ivermectin, is a growing concern in livestock.
- Understanding the impact of resistance on parasite pathogenicity is crucial for effective control.
Purpose of the Study:
- To investigate the effects of benzimidazole-resistant and multi-drug resistant Teladorsagia circumcincta isolates on lamb liveweight gain and immune development.
- To compare the pathogenicity and immunogenicity of resistant isolates against a susceptible isolate.
- To determine if genetic alterations for anthelmintic resistance affect parasite virulence.
Main Methods:
- Lambs were trickle infected for 8 weeks with susceptible (MOSI), benzimidazole-resistant (MORI), or multi-drug resistant (MCRI) Teladorsagia circumcincta isolates.
- Liveweight gain, plasma pepsinogen, and fecal consistency were monitored.
- Fecal egg counts (FECs) and pre-patent periods were assessed.
- Worm burden and mucosal mast cell numbers were evaluated post-anthelmintic treatment.
Main Results:
- Plasma pepsinogen increased significantly in infected lambs by day 14.
- No significant differences in liveweight gain were observed between infected and control groups.
- Lambs infected with MORI showed reduced fecal consistency initially, but this normalized later.
- Pre-patent periods varied, with MOSI showing earlier positive FECs.
- No differences in worm burden or mast cell numbers were found after anthelmintic treatment.
Conclusions:
- Genetic changes conferring anthelmintic resistance in Teladorsagia circumcincta do not appear to fundamentally alter pathogenicity or immunogenicity.
- Resistant parasite isolates did not cause significant differences in liveweight gain or overall immune response compared to susceptible isolates in this study.
- Further research may be needed to fully elucidate the long-term impacts of anthelmintic resistance on host-parasite dynamics.