In vitro characterization of anthelmintic susceptibility of field isolates of the pig nodular worm Oesophagostomum spp., susceptible or resistant to various anthelmintics.

A larval development assay (LDA) and an egg hatch paralysis assay (EHPA) were used to measure the sensitivity to anthelmintics of eggs and larvae of nodular worms (Oesophagostomum spp.) in pigs. The tests were carried out using in vivo defined resistant and susceptible isolates of Oesophagostomum dentatum, O. quadrispinulatum and Oesophagostomum spp. For measurement of pyrantel/morantel and levamisole sensitivity the LDA was found able to distinguish between susceptible or resistant isolates of Oesophagostomum. The EHPA was able to detect levamisole resistance, but the test failed to show differences in response to pyrantel between pyrantel susceptible and resistant lines. The possible routine application of LDA and EHPA in the diagnosis of anthelmintic resistance in Oesophagostomum spp. is discussed.