Closantel resistance in Huemonchus contortus from sheep

Resistance to macrocyclic lactone anthelmintics byHaemonchus contortusandOstertagia circumcinctain sheep in New Zealand

“…Certainly, support for this suggestion may be provided by a number of other instances in which resistance to the former drug has been accompanied by a reduced therapeutic efficacy of the latter (Pomroy and Whelan, 1993;Leathwick, 1995;Watson et al, 1996;Bridi et al, 1997;Sutherland et al, 1999) and by the results of the present study where moxidectin, despite maintaining an apparently high therapeutic efficacy, was found to exhibit a reduction in its prophylactic activity. This latter result may not be altogether surprising since, in the case of persistent anthelmintics, resistance may be expressed either as a diminished ability to remove worms present at the time of treatment or as a reduction in residual efficacy (Rolfe et al, 1990). Indeed, it is reasonable to expect that, for persistent anthelmintics such as moxidectin, a loss or reduction in prophylactic activity is likely to be the first expression of resistance to them (Rolfe and Fitzgibbon, 1996).…”

Reduced efficacy of ivermectin, abamectin and moxidectin against field isolates of Haemonchus contortus

“…With closantel resistance there is a reduced period of protection against H contortus after treatment and this adds complexity to control programs. 5,9 Moxidectin and ivermectin, when incorporated in controlledrelease capsules, are the only other formulations registered in Australia with a claim for persistent efficacy against H contortus and thus there is a temptation to utilise these products to maintain control in the face of closantel resistance. This will increase the exposure of the entire nematode population to products in the ML group.…”

The use of DNA markers to map anthelmintic resistance loci in an intraspecific cross ofHaemonchus contortus

“…Wallangra1984 -18 years prior to the isolation of Wallangra2003, this isolate was obtained from the same farming enterprise and closantel resistance was evident at that time (Rolfe et al 1990). The isolate might be regarded as ancestral to Wallangra2003 ; however, extensive migration facilitated by stock movement cannot be excluded as a factor that affected the population over the intervening period.…”

“…(Le Jambre et al 1976, 1979Webb et al 1979 ;Edwards and Chaneet, 1980 ;Green et al 1981 ;Rolfe, 1990 ;Sangster and Bjorn, 1995 ;Dobson et al 2001 ;Kotze et al 2002 ;Besier and Love, 2003). In Australia, the main nematodes causing production loss are Teladorsagia circumcincta, Trichostrongylus spp.…”