Quantitative molecular diagnosis of levamisole resistance in populations of Haemonchus contortus

• Published in: Experimental parasitology Vol. 205; p. 107734
• Main Authors: Santos, Jessica Maria Leite dos, Vasconcelos, Janaélia Ferreira, Frota, Gracielle Araújo, Freitas, Edilson Pereira de, Teixeira, Marcel, Vieira, Luiz da Silva, Bevilaqua, Claudia Maria Leal, Monteiro, Jomar Patrício
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-10-2019
• Subjects: Anthelmintic resistance; Levamisole; Nematode parasite; Real-time PCR; Sheep; Anthelmintic resistance; Sheep; Real-time PCR; Nematode parasite; Levamisole
• ISSN: 0014-4894; 1090-2449
• DOI: 10.1016/j.exppara.2019.107734

Parasitism by Haemonchus contortus is one of the main limiting factors in small ruminant production around the globe. Although several studies suggest the use of integrated management practices, these parasites have been controlled essentially with synthetic anthelmintic drugs. The resistance mechanism against the imidazothiazole derivative levamisole in Haemonchus contortus has not been fully described. Recently, resistance was associated with a 63bp deletion in the Hco-acr-8b gene that encodes a subunit for a nicotinic acetylcholine receptor. This study aimed to standardize a real time PCR (qPCR) protocol for levamisole resistance diagnosis in H. contortus populations based on this polymorphism and use it to characterize 23 field H. contortus populations obtained from different localities of Ceará State, Northeast Brazil. In addition, two populations of H. contortus were used as a standard of susceptibility and resistance, Inbred Strain Edinburgh (ISE) and Kokstad, respectively. Larval development tests (LDT) were performed on five field isolates and both EC50 and EC95 were estimated. LDT EC95 values provided a wider interval between susceptible and resistant populations than EC50 values (EC95 = 1.96–57.93 μM; EC50 = 0.05–0.39 μM), and were found to be more appropriate for differentiating them. Real time PCR results showed resistance allele frequencies ranged from 20.9 to 76.7%. Our results suggest that levamisole resistance may be present in field populations but it is not as widespread as benzimidazole resistance. This methodology may be useful to monitor levamisole resistance in field populations of H. contortus.
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•The qPCR assay successfully detected the 63 bp indel in the Hco-acr-8 gene.•Significant correlation was verified among LDT and qPCR.•The resistance to levamisole is not as widespread as is the case with benzimidazoles.