Characterization of moxidectin resistant Trichostrongylus colubriformis and Haemonchus contortus.
The development of moxidectin resistance (MOX-R) in sheep parasitic gastrointestinal nematodes already carrying multiple resistances to other anthelmintic groups has made control of these strains very difficult. The anthelmintic resistance patterns of MOX-R strains of Trichostrongylus colubriformis and Haemonchus contortus were characterized to provide an insight into the remaining role of anthelmintics in the control of such strains. Homozygous MOX-R individuals of both genera were unaffected by moxidectin. For MOX-R heterozygotes a dose rate of 200 microg/kg abamectin (ABA) given orally removed 25% of H. contortus while 200 microg/kg MOX given orally achieved a 72% reduction. Doubling the dose rate of ABA improved the mean efficacy to 37%. Consequently, in H. contortus, the degree of dominance differs markedly between the two anthelmintics. A dose rate of 8 mg/kg levamisole and 185 mg/kg napthalophos achieved >95% reduction in worm count of the MOX-R homozygous H. contortus but only 85 and 7%, respectively against the MOX-R homozygous T. colubriformis.
Le Jambre
L F
LF
CSIRO Livestock Industries, Locked Bag 1, Armidale, NSW 2350, Australia. leo.lejambre@csiro.au
Geoghegan
J
J
Lyndal-Murphy
M
M
D000018:Abomasum / Q000469:parasitology; D000284:Administration, Oral; D000818:Animals; D000871:Anthelmintics / Q000627:therapeutic use*; D004351:Drug Resistance; D005243:Feces / Q000469:parasitology; D005260:Female; D006188:Haemonchiasis / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D006189:Haemonchus / Q000235:genetics / Q000254:growth & development*; D007559:Ivermectin / Q000031:analogs & derivatives* / Q000627:therapeutic use; D007978:Levamisole / Q000627:therapeutic use; D018942:Macrolides / Q000627:therapeutic use*; D008297:Male; D009943:Organophosphorus Compounds / Q000627:therapeutic use; D010270:Parasite Egg Count / Q000662:veterinary; D011793:Queensland; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy* / Q000469:parasitology*; D014253:Trichostrongylosis / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D014254:Trichostrongylus / Q000235:genetics / Q000254:growth & development*
D000871:Anthelmintics; D018942:Macrolides; D009943:Organophosphorus Compounds; D007978:Levamisole; C048324:abamectin; D007559:Ivermectin; C008897:naftalofos; C027837:moxidectin