Article

Phenotypic and genotypic characterisation of benzimidazole susceptible and resistant isolates of Haemonchus contortus

Parasitological Institute, Slovak Academy of Sciences, Hlinkova 3, 040 01 Kosice, Slovak Republic.
Veterinary Parasitology (Impact Factor: 2.55). 08/2010; 172(1-2):155-9. DOI: 10.1016/j.vetpar.2010.04.022
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ABSTRACT The study was designed to compare the in vitro egg hatch test (EHT) and molecular allele-specific polymerase chain reaction PCR (AS-PCR) methods as tools for detection of benzimidazole resistance in Haemonchus contortus, a nematode parasite of small ruminants. Comparisons were made during the course of an experimental infection and changes in EHT and AS-PCR were monitored to measure the correlation between in vitro and molecular tests. Both methods were carried out according to World Association for the Advancement of Veterinary Parasitology (WAAVP) recommendations. The molecular test was used to discriminate TAC/TTC polymorphism in the beta-tubulin 200 codon of eight (four resistant and four susceptible) isolates of H. contortus. Using DNA from 100 third-stage larvae, the polymerase chain reaction (PCR)-based analysis revealed a decrease of the homozygous TTC/TTC genotype and an increase in heterozygous TTC/TAC and homozygous TAC/TAC individuals in all resistant isolates. Both methods showed comparable and reliable results with regard to detection of benzimidazole resistance. The molecular test has an advantage over the EHT because of its higher sensitivity. On the other hand, EHT is less time-consuming, allows reliable detection of <10% resistance allele frequency and is fairly reliable for the detection of benzimidazole resistance under field conditions.

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    • "Effective monitoring of resistance is vital for maintaining a high efficacy of the currently available anthelmintics and for preventing further selection for resistance, especially in areas where AR is present in only a small proportion of the worm population. The use of a discrimination/delineating dose (DD) in the EHT provides a good estimate of genotypic resistance [14]. The egg hatch discrimination dose test (EHDDT) is less time-consuming, allows the reliable detection of a frequency of resistance alleles below 10% and is fairly reliable for the detection of BZ resistance under field conditions [14]. "
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