Genetic Approaches to Identify Loci Linked to the Anthelmintic Resistance in Haemonchus Contortus Evidence for the genetic linkage of three microsatellite makers to an ivermectin resistance locus in the genetic F2 crossing of Haemonchus contortus strains (Anthelmintics - From Discovery to Resistance III Indian Rocks Beach, FL, USA)

  • Umer Naveed Chaudhry (Speaker)

Activity: Academic talk or presentation typesOral presentation


Genetic crosses were undertaken between the anthelmintic sensitive genome strain of H. contortus-MHco3 (ISE) and a multi-drug resistant strain-MHco18 (UGA) derived from southern USA. One hundred female (MHco3) and 100 male (MHco18) and vice versa immature day 14 post infection larvae were surgically transferred to the abomasa of recipient sheep. The F1 L3 larvae recovered from coprocultures were used to orally infect another donor sheep to obtain F2 progeny, which was then selected with three anthelmintic drug classes [Ivermectin (IVM), Benzimidazoles (BZ) and Levamisole (LEV)] to produce drug selected F2 populations. Sensitivity of the BZ drug in parental strains, F1/F2 progeny and BZ selected F2 populations have been genotypically assessed using three known isotype-1 β tubulin SNPs [F167Y (TAC, E198A (GCA), F200Y (TAC)]. The data gives strong evidence for the transfer of BZ resistance mutations from the resistant parental strain to F1 & F2 progeny followed by an increase of resistance allele frequency in the BZ selected F2 population. The genotyping of parental strains, F1 progeny and the drug selected F2 populations using a panel of 6 microsatellites markers, was used to monitor the success of the genetic crossing procedure. The alleles from all 6 microsatellites were scored as being present or absent in genotypes derived from the parental strains, F1 progeny and drug selected F2 populations. The IVM selected F2 population was further analyzed with the Hcms8a20 marker either excluded or included, since this marker shows evidence of an association with ivermectin resistance conferring locus in chromosome V. Further investigations were undertaken with a panel of 8 new microsatellite markers located in chromosome V in the IVM selected F2 population, to look for evidence of genetic linkage to IVM resistance conferring loci, providing a starting point for more detailed studies to identify the mutations linked to IVM resistance. The data were presented based on the presence and absence of strain specific alleles. Two markers (Hcms3520, Hcms3775) in addition to Hcms8a20 were retained after IVM treatment, giving strong evidence of the linkage of an IVM resistance conferring locus.
Event titleAnthelmintic Resistance III USA
Event typeConference
LocationUnited States