Intergeneric relations between nematodes of the digestive tract in lambs: a multivariate approach

The interactions between nematode genera of the ovine digestive tract have been examined through a multivariate analysis performed on data previously obtained in epidemiological surveys conducted in France and Morocco. Data referring both to the frequency of genera per sheep (analysis at the individual level) and to the number of worms per genus and per animal (analysis at the host population level) were examined. The results suggest that a highly stable equilibrium between genera occurred in individual hosts possibly regulated by the host response and the interactions between the worm populations. The regulative factors which act at the host population level tend to increase the stability of the system, to promote the expression of positive interactions between the genera and also to modulate the arrangement of intergeneric relations. The multivariate analysis thus provides a means for global analysis of the relations between nematode populations with potential applications to assess the efficacy of some control measures on the whole nematode community in the digestive tract.