An Epidemiological Investigation and Drug-Resistant Strain Isolation of Nematodirus oiratianus in Sheep in Inner Mongolia, China

SIMPLE SUMMARY: Nematodirus has a serious impact on the gastrointestinal health of ruminants and the economic development of animal husbandry. This study investigated Nematodirus infections of different rearing patterns in sheep in two well-known natural pastures in Inner Mongolia, China. The results indicated that the average infection rate was more than 50%. Then, a naturally occurring strain of Nematodirus was obtained by using numerous isolation methods. We recorded the detailed development process of the nematode eggs and tested for drug resistance, and the results showed that the isolated strains were found to be ivermectin-resistant strains. Our study provides useful data for the morphological study of Nematodirus and the prevention and control of nematodes, offering valuable species resources for studying anthelmintic resistance in nematodes. ABSTRACT: Nematodirus causes major economic losses in the development of the livestock industry, as they are common gastrointestinal parasites of cattle, sheep, and other ruminants. The present study investigated Nematodirus infections in sheep in the Hulunbuir and Xilingol Grasslands, two well-known natural pastures in Inner Mongolia, China. The results indicated that the average infection rate was more than 50%. Furthermore, a naturally occurring strain of Nematodirus was obtained using numerous isolation methods in the survey region. Conventional morphology and molecular biology were used to identify the strain. The larval migration inhibition test was used to determine the ivermectin level in the isolated strain. The results indicated that the larvae belonged to the species Nematodirus oiratianus. The strain was found to be ivermectin-resistant. Thus, these results recorded the detailed development processes of Nematodirus eggs, providing novel insights regarding the prevention and control of nematodes by using conventional anthelmintic regimens and by offering valuable species resources for studying anthelmintic resistance in nematodes.