Detection of drug resistance in the sheep nematode «haemonchus contortus»
Notice bibliographique
Résumé
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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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».