P-glycoprotein gene expression analysis of ivermectin resistance in sheep naturally infected with Haemonchus contortus

The upregulation of P-glycoprotein genes in Haemonchus contortus suspected of ivermectin resistance (IVM-Res) was studied in sheep farms. A faecal egg count reduction test (FECRT) was used to evaluate IVM-Res on four farms (from A to D). Faecal samples positive to gastrointestinal nematodes (GINs) were used to identify infective larval stages (L3) pre- and post-IVM treatment by Polymerase Chain Reaction (PCR) test. Ten P-glycoprotein (pgp) genes were analysed to estimate the over expression level in H. contortus L3. Genes were quantified using the Retro Transcription–real time PCR technique. FECRT indicated low IVM efficacy on the four farms from zero to 33% of eggs per gram and Haemonchus, Cooperia and Trichostrongylus were the GINs identified after IVM treatment. H. contortus isolates displayed different pgp gene upregulation levels (p < 0.05): pgp4 from 19.03 to 25.96-fold on four farms; 3 and 16 pgp from 32.19 to 134.21-fold on three farms; 1, 2 and 12 pgp from 7.14 to 56.43-fold on two farms; 10 and 11 pgp from 6.82 to 32.86-fold on one farm. In conclusion, the examination of FECRT showed low IVM efficacy against GINs. Additionally, pgp3, 4 and 16 were the most frequent genes involved in sheep farms with IVM-Res problems in relation to IVM resistant H. contortus.