Different levels of anthelmintic resistance in the facultative parasitic nematode Halicephalobus gingivalis

Abstract

In recent years many studies have proven that most equine parasites have some form of resistance to all main classes of anthelmintic drugs. However, studies on anthelmintic resistance in equine parasites only include obligatory parasites, not facultative parasites. Halicephalobus gingivalis is a free-living bacteriovorous nematode and a known facultative parasite of horses. In all reported infections the horses were regularly treated with common anthelmintics, strongly indicating the possibility that H. gingivalis has some form of resistance to these anthelmintic drugs. We present the results of an in vitro study on the resistance of several isolates of H. gingivalis, both free-living and parasitic. All were tested in vitro for the extent of their resistance to two different anthelmintic drugs, ivermectine and thiabendazole, using an adaptation of the micro-agar larval development test and focusing on egg hatching and larval development. Main conclusion is that the anthelmintic resistance of H. gingivalis was considerably higher than that of closely related panagrolaimid nematode species, with the parasitic isolates having a higher resistance than the free-living ones