ACETYLCHOLINESTERASE IN INFECTIVE-STAGE LARVAE OF HAEMONCHUS-CONTORTUS, OSTERTAGIA-CIRCUMCINCTA AND TRICHOSTRONGYLUS-COLUBRIFORMIS RESISTANT AND SUSCEPTIBLE TO BENZIMIDAZOLE ANTHELMINTICS

The amounts of acetylcholinesterase (AChE) in homogenates of infective -stage larvae of strains, from different countries, of Haemonchus cont ortus, Ostertagia circumcincta and Trichostrongylus colubriformis resi stant or susceptible to benzimidazole (BZ) anthelmintics, were compare d using a rapid colorimetric assay. The levels of AChE were much great er in those strains which were BZ-resistant than in BZ-susceptible pop ulations. The larvae of susceptible and resistant H. contortus contain ed less AChE than did the larvae of the other two species. One-way ana lysis of variance showed that the observed differences between suscept ible and resistant strains were significant in each of the species stu died. It is suggested that the extra enzyme may act as an anthelmintic -detoxifying enzyme, may inactivate the active site of the anthelminti c or may prevent binding of the anthelmintic to its receptor.