South African field strains of Haemonchus contortus resistant to the levamisole/morantel group of anthelmintics.
A strain of Haemonchus contortus from the Pietermaritzburg district of Natal was found to be resistant to levamisole (geometric mean efficacy 76.5%), morantel (41.9%), the benzimidazoles (oxfendazole: 33.7%) and rafoxanide (82.0%), but apparently fully susceptible to closantel and disophenol. In the case of ivermectin, a mean of 5.2% of the H. contortus was not removed at a dosage of 200 micrograms kg-1 live mass. A second strain of H. contortus, from Amsterdam in the south-eastern Transvaal, showed reduced susceptibility to levamisole (80.8%) and morantel (46.2%), the only 2 drugs tested. This is apparently the first report of resistance to the levamisole/morantel group of anthelmintics in sheep in South Africa.
van Wyk
J A
JA
Veterinary Research Institute, Onderstepoort, Republic of South Africa.
van Schalkwyk
P C
PC
Gerger
H M
HM
Visser
E L
EL
Alves
R M
RM
van Schalkwyk
L
L
D000818:Animals; D000871:Anthelmintics / Q000627:therapeutic use*; D002986:Clinical Trials as Topic; D004351:Drug Resistance; D006188:Haemonchiasis / Q000188:drug therapy / Q000662:veterinary*; D006189:Haemonchus / Q000187:drug effects*; D007978:Levamisole / Q000494:pharmacology / Q000627:therapeutic use*; D009015:Morantel / Q000494:pharmacology / Q000627:therapeutic use*; D011743:Pyrimidines / Q000627:therapeutic use*; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy*; D014251:Trichostrongyloidea / Q000187:drug effects*; D014252:Trichostrongyloidiasis / Q000662:veterinary*
D000871:Anthelmintics; D011743:Pyrimidines; D007978:Levamisole; D009015:Morantel