Efficacy of some anthelmintics on an ivermectin-resistant strain of Haemonchus contortus in sheep.
Following evidence of reduced efficacy of ivermectin in a field population of Haemonchus contortus in Brazil, this strain of the parasite was submitted to a controlled anthelmintic test. Eighty worm-free lambs were randomly split into two groups of 40. Each lamb in the first group was infected with 5000 third stage larvae (L3) of the ivermectin-resistant strain; the remaining 40 lambs were each infected with 5000 L3 of a H. contortus strain of known susceptibility to the major groups of anthelmintic compounds used in sheep. On Day 28 post-infection, each group was subdivided according to egg counts and at random into four sub-groups of ten lambs, each of which was treated with albendazole (ABZ) at 3.8 mg kg-1, levamisole (LEV) at 7.5 mg kg-1 or ivermectin (IVM) at 0.2 mg kg-1, or was left as untreated control. At slaughter, 7 days later, all the anthelmintics reduced worm burdens in animals infected with the susceptible strain (ABZ 98.9%, LEV and IVM 100%). By contrast, in the lambs infected with the ivermectin-resistant strain, LEV was 99.8% effective, but ABZ reduced worm counts by only 14.7% and IVM by only 10.4%. Interestingly at necropsy on Day 7 post-treatment, the egg counts in the resistant strain treated with ABZ had been reduced by 92.5%, although worm counts were reduced by only 14.7%.(ABSTRACT TRUNCATED AT 250 WORDS)
Echevarria
F A
FA
Department of Veterinary Parasitology, University of Glasgow, UK.
Armour
J
J
Duncan
J L
JL
D015766:Albendazole / Q000494:pharmacology / Q000627:therapeutic use; D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology / Q000627:therapeutic use*; D004351:Drug Resistance; D005243:Feces / Q000469:parasitology; D006188:Haemonchiasis / Q000188:drug therapy / Q000662:veterinary*; D006189:Haemonchus / Q000187:drug effects*; D007559:Ivermectin / Q000494:pharmacology* / Q000627:therapeutic use; D007978:Levamisole / Q000494:pharmacology / Q000627:therapeutic use; D010270:Parasite Egg Count / Q000662:veterinary; D011897:Random Allocation; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy*
D000871:Anthelmintics; D007978:Levamisole; D007559:Ivermectin; D015766:Albendazole