Larval Migration and Inhibition Assay (LMIA) The In Vitro Selection and Differentiation of Moxidectin Resistant Larvae of Sheep

Abstract

Abstract Resistance to anthelmintics is an increasing problem in the sheep industry worldwide. The intensive use of anthelmintics has led to selection of resistant worms affecting sheep populations. Therefore it is important to monitor the efficacy of anthelmintics that are available. Also it is important to be able to detect resistance against anthelmintic drugs at low levels in order to change parasite management and to determine which drug classes still remain effective against certain nematode populations. The Larvae Migration Inhibition Assay (LMIA) can be used to indicate resistance against the anthelmintic drug moxidectin. The LMIA makes use of the paralytic effect of moxidectin on susceptible larvae. Susceptible larvae become irreversibly paralyzed and die when incubated with moxidectin and therefore these larvae are not able to migrate through sieves. Larvae that are less or not susceptible to moxidectin will still be able to migrate through these sieves. This basic assumption is used in the LMIA to make a distinction between susceptible and not susceptible larvae. This study focussess on the LMIA as a method for detecting larval migration of gastro intestinal nematodes of sheep by looking at percentage migration of larvae in a dilution series from a high to a low moxidectin concentration.