Multiple species of nematodes resistant to ivermectin and a benzimidazole-levamisole combination on a sheep farm in New Zealand.
OBJECTIVE
To confirm the presence of multiple anthelmintic resistance on a sheep farm in New Zealand.


METHODS
Three groups of 10 weaned Romney-cross lambs were treated either with an oral dose of ivermectin (0.2 mg/kg), or a benzimidazole/levamisole (BZ/LEV) combination (4.75 albendazole and 7.5 mg/kg levamisole), or were left untreated. Ten days later, animals were necropsied, and adult worms recovered and identified from the abomasa and small intestines. Pre- and post-treatment faecal nematode egg counts (FEC) were recorded, and larval cultures were performed.


RESULTS
In a faecal egg count reduction test (FECRT), adjusted to reflect pre- and post-treatment larval culture results, ivermectin resistance was detected in Teladorsagia (Ostertagia), Trichostrongylus and Haemonchus spp, while BZ/LEV combination- resistant Teladorsagia and Trichostrongylus spp were also present. Adult worm counts confirmed these results, and identified the species involved as Teladorsagia circumcincta, Trichostrongylus colubriformis and H. contortus.


CONCLUSIONS
Multiple, multi-generic anthelmintic resistance was confirmed on a sheep property in New Zealand. This included the first confirmed case of ivermectin resistance in T. colubriformis from sheep in New Zealand.
Sutherland
I A
IA
AgResearch, Hopkirk Institute, Palmerston North, New Zealand. ian.sutherland@agresearch.co.nz
Damsteegt
A
A
Miller
C M
CM
Leathwick
D M
DM
D000284:Administration, Oral; D000818:Animals; D000831:Animals, Newborn; D000871:Anthelmintics / Q000008:administration & dosage / Q000627:therapeutic use*; D001562:Benzimidazoles / Q000008:administration & dosage / Q000627:therapeutic use; D004351:Drug Resistance; D004359:Drug Therapy, Combination; D005243:Feces / Q000469:parasitology; D005260:Female; D006374:Helminthiasis, Animal / Q000188:drug therapy* / Q000469:parasitology; D007559:Ivermectin / Q000008:administration & dosage / Q000627:therapeutic use; D007978:Levamisole / Q000008:administration & dosage / Q000627:therapeutic use; D008297:Male; D009520:New Zealand / Q000453:epidemiology; D010270:Parasite Egg Count / Q000662:veterinary; D021261:Parasitic Sensitivity Tests / Q000662:veterinary; D015995:Prevalence; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy* / Q000469:parasitology; D016896:Treatment Outcome
D000871:Anthelmintics; D001562:Benzimidazoles; D007978:Levamisole; D007559:Ivermectin; C031000:benzimidazole