A Labratory Survey on Drug Resistance in Gastrointestinal Nematodes of Sheep in Iran

Broad spectrum anthelmintics had been used for about 50 years to control internal parasites of human and animals. In this survey, resistance in gastrointestinal nematode of sheep to levamisole and albendazole were investigated in 15 sheep flocks. On each flock, faecal samples were taken from 20 randomly selected sheep. Nematode eggs were separated from the samples and placed in microplate for 24 hours at 25 °C to hatch and then Nutritive media, Escherichia coli and different concentrations of levamisole or albendazole were added to first stage larvae and incubated at 25 °C for 6 more days. LD50 of these drugs in each flock were calculated according to precent of larval development parameter in different concentration of levamisole or albendazole (Hubert and Kerboeuf, 1992). LD50 of levamisole were varied between 0.021 to 0.27 μg /ml and LD50 of albendazole between 0.021 to 0.13 μg/ml. In negative control samples with no anthelmintic average larval development was 65% and third stage larvae were mostly composed of Ostertagia (59%), Trichostrongylus (20%) and Haemonchus (21%) but in positive contol samples with the highest concentration of levamisole Ostertagia spp and Trichostrongylus spp and albendazole Ostertagia spp were detected. Therefore we can conclude that resistance have been developed in some isolates of Ostertagia spp and Trichostrongylus spp to levamisole and to in some isolates of Ostertagia spp to benzimidazoles that can be alarming for treatment of trichotrongylus in people.