Abstract
Considerable research has been directed towards optimising in vitro tests that can diagnose resistance in pre-parasitic stages of parasites. The objective of this study was to compare the in vivo faecal egg count reduction test (FECRT), the in vitro egg hatch test (EHT), and the molecular determination of the frequency of a codon 200 allele of β-tubulin isotype 1 associated with benzimidazole resistance in larval stages of Haemonchus contortus obtained from infected goats. Animals were infected with composite infective doses representing 10, 20, 30, 40, 60, and 80% resistant alleles. Faecal samples for the EHT were collected on 28, 33, and 35 days post-infection. The results of the in vivo FECRT indicated that albendazole treatment reduced infections consisting of composite doses of 10, 20, 30, 40, 60, and 80% larvae of the resistant isolate by 91.3, 78.0, 63.3, 48.4, 36.5, and 41.4%, respectively. The drug concentration at which 50% of the eggs were prevented from developing hatching larvae (ED50) in the in vitro EHT varied from 0.09 ± 0.01 to 15.63 ± 12.10 μg/mL thiabendazole. The results of the in vitro EHT indicated that the test could estimate in vivo resistance well. The EHT could thus accurately estimate the in vivo efficacy of the drug and percentage of the resistance allele in the population using hatching parameters in delineation doses. This finding was also supported by comparing the FECRT data to the hatching percentages in the EHT on 30 goat farms in Slovakia with natural mixed infections of gastrointestinal parasites.
Highlights
The efficient use of anthelmintics is an integral part of worm control strategies for preventing production losses from parasitic infections
The percentages of the TAC allele of b-tubulin isotype 1 were very similar with the estimated percentages of resistant larvae in the infective doses in each group of goats
The results of the faecal egg count reduction test (FECRT) were comparable with the genotypes of the L3 larvae derived from the worms used to infect the animals
Summary
The efficient use of anthelmintics is an integral part of worm control strategies for preventing production losses from parasitic infections. The intensive and/or inappropriate use of anthelmintics, leads to the development of anthelmintic resistance (AR), which has become important in most countries with intensive productions of small and large ruminants [33]. The accurate diagnosis of resistance in these countries would help to prevent AR from becoming widespread. The egg hatch test (EHT) and larval development test are the most frequently used in vitro methods for detection of BZ resistance. Both in vitro tests have demonstrated comparable and reliable results for detecting BZ resistance and have an advantage over other techniques due to their higher sensitivity in identifying relatively small proportions (4%) of resistant worms in a population [28]. The main disadvantage of the FECRT and EHT is that they can only detect resistance when >25% of a nematode population contains the resistance allele [20]
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