Hybridization, high genetic diversity, and molecular evidence of drug resistance to albendazole and levamisole in Haemonchus populations infecting goats in Thailand

Abstract

Background: Haemonchosis, due to infection with Haemonchus contributes to livestock morbidity globally, resulting in economic losses. Hybrids between Haemonchus contortus and H. placei have been evidenced, where sharing of hosts, geographical sympatry, and farming practices allow opportunities for hybridization. In Thailand, high prevelances of H. contortus infecting goats have been documented, and high levels of drug resistance are strongly suspected, due to unregulated and widespread use of anthelmintics (e.g. benzimidazoles and imidazothiazoles). Moreover, the exchange of genetic material facilitates the spread of anthelmintic resistance. Here, we aim to identify the Haemonchus species infecting goats, investigate their population genetic structure, and assess anthelmintic resistance to albendazole and levamisole. Results: Using 188 Haemonchus adults obtained from goats across six provinces in Thailand, molecular identification was performed using the nuclear ITS2 region. The population genetic structure was investigated by amplifying the mitochondrial COI gene of representative H. contortus specimens. Genotypic resistance to albendazole and levamisole resistance status were assessed via the single-nucleotide polymorphisms in the β-tubulin and hco-acr-8 gene, respectively. Of the specimens, 97.3% were molecularly identified as H. contortus, while 2.7% were potential hybrids between H. contortus and H. placei. Hybrids were identified in Nakhon Pathom, Kanchanaburi, Ratchaburi, and Suphanburi provinces. The population genetic structure of H. contortus revealed high genetic diversity, high gene flow, and low genetic differentiation between populations. High levels of albendazole resistance were detected, with an overall frequency of 0.56 and 0.44 for the susceptible and resistant alleles, respectively. Compared to albendazole, lower levels of levamisole resistance were obtained, with an overall frequency of 0.87 and 0.13 for the susceptible and resistant alleles, respectively. Conclusions: This study revealed the hybrid form of H. contortus and H. placei in goats, high genetic diversity of H. contortus populations, and the presence of albendazole and levamisole resistance. The growing challenge of drug resistance and hybridization in Haemonchus populations demonstrates the urgent need for regulated drug use and the implementation of sustainable management practices.