Confirmation of resistance to ivermectin by Cooperia curticei in sheep.
OBJECTIVE
To investigate the occurrence of resistance to a full dose of oral ivermectin by Cooperia curticei in sheep.


METHODS
Twelve lambs on a sheep and cattle property in the North Island of New Zealand were randomly allocated to one of two equal-sized groups. One group was treated orally with a single dose of ivermectin at the manufacturer's recommended dose rate of 0.2 mg/kg, while the other remained as an untreated control. Worm counts were carried out post mortem on the abomasa and small intestines of all animals in both groups 7 days after treatment.


RESULTS
While treatment with ivermectin reduced the numbers of all other worm genera to almost zero, those of Ostertagia(= Telodorsagia) circumcincta and C. curticei were reduced by only 37% and 19%, respectively.


CONCLUSIONS
These results provide clear evidence of resistance to ivermectin by O. circumcincta and C. curticei. They also appear to represent the first record of macrocylic lactone (ML) resistance in C. curticei in sheep in New Zealand or elsewhere.
Hughes
P L
PL
Taihape Veterinary Services Limited, Taihape, New Zealand.
McKenna
P B
PB
D000018:Abomasum / Q000469:parasitology; D000284:Administration, Oral; D000818:Animals; D000969:Antinematodal Agents / Q000494:pharmacology*; D004351:Drug Resistance; D007559:Ivermectin / Q000494:pharmacology*; D009520:New Zealand / Q000453:epidemiology; D010028:Ostertagia / Q000187:drug effects / Q000254:growth & development; D010029:Ostertagiasis / Q000188:drug therapy / Q000662:veterinary; D011897:Random Allocation; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy*; D016896:Treatment Outcome; D014251:Trichostrongyloidea / Q000187:drug effects* / Q000254:growth & development; D014252:Trichostrongyloidiasis / Q000188:drug therapy / Q000662:veterinary*
D000969:Antinematodal Agents; D007559:Ivermectin