Detection of drug resistance in the sheep nematode «haemonchus contortus»
Bibliographic record
Abstract
Small ruminants are naturally infected with gastro-intestinal nematodes while grazing. Once ingested, Haemonchus contortus contaminates the sheep abomasum. This nematode feeds on its host’s blood and causes prodigious losses in sheep industries. Farmers have been using anthelmintic drugs for many years to remove parasitic infections and this intensive use has led to drug resistance in the nematode. Resistance to benzimidazole, ivermectin or levamisole have been reported in most of the areas where H. contortus is present. Drug resistance represents a real threat to sheep industries. The benzimidazole-resistance mechanism has been described at the molecular level; it involves three mutations of the β-tubulin isotype 1 gene at codons 167, 198 or 200. To characterize these mutations in resistant parasites, we genotyped individual H. contortus that survived an increase in the dose rate of benzimidazole. The resistant allele at codon 200 was found in parasites that survived the normal and the highest dose rate of drug tested. We proposed to detect resistance to benzimidazole with the H. contortus egg genetic profiles from the field. To be certain of the relevance of the genetic test, it was necessary to prove that it would give similar results to the tests usually used and that it had benefits compared to others tests. For this purpose, two field studies took place: the first field study was a collaboration with Dr Andrew Peregrine (Guelph University, Ontario, Canada) and the second was performed in Quebec. Benzimidazole resistance was found in Ontario and in Quebec in H. contortus. The genetic test gave similar results to Fecal Egg Count Reduction Test but it was faster, less expensive, more precise and could detect resistance in a pool of eggs collected in fecal samples. The application of this test can be achieved before treatment and the efficacy of the drug can be predicted before drenching the flock. This represents a considerable saving of money and time. The success we had with the genetic test to detect benzimidazole resistance led us to look for similar resistance markers in the H. contortus genome for ivermectin resistance.The gene Hco-avr-14b encodes a subunit of a glutamate-gated chloride channel; the coding and non-coding regions of this gene were screened in H. contortus field isolates with different responses to ivermectin treatment to highlight mutations linked to ivermectin resistance. We did not find markers of ivermectin resistance in the Hco-avr-14b gene. Studies presented a relationship between levamisole resistance and the gene Hco-acr-8 coding for a subunit in a levamisole-sensitive acetylcholine receptor in H. contortus. This gene was analysed in H. contortus field isolates with different responses to levamisole and several interesting patterns were found. However, markers to detect levamisole resistance were not found in the gene Hco-acr-8.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".