Emergence of dual drug-resistant strongylids in goats: first phenotypic and genotypic evidence from Ratchaburi Province, central Thailand.

Background: This study provides crucial insights into the prevalence and drug resistance patterns of strongylid gastrointestinal nematodes (GINs) in goats in Thailand, highlighting resistance to albendazole and levamisole. Strongylids, particularly Haemonchus sp. and Trichostrongylus sp., pose a significant threat to goat health. With the global rise of anthelmintic resistance, the detection of multidrug resistance in Thailand's goat population is concerning, given the frequent import and export of goats. This resistance challenges effective parasite control strategies. This study aimed to identify strongylid species using both morphological and genetic methods and to assess resistance to albendazole and levamisole through phenotypic and molecular approaches.

Results: Fecal samples from 30 goat farms in Ratchaburi Province revealed a high prevalence of strongylid infection (87%), with Haemonchus sp. and Trichostrongylus sp. detected on 100% and 96% of farms, respectively. Phenotypic assays demonstrated significant drug resistance, with 90% and 71% of farms harboring strongylid populations resistant to albendazole and levamisole, respectively. Genotypic analysis of pooled infective larvae showed that 100% of farms had albendazole-resistant strongylid populations, with 31% homozygous and 69% heterozygous resistance, and Trichostrongylus sp. showing 48% homozygous and 52% heterozygous resistance. For levamisole resistance, 92% of farms contained resistant strongylid populations, with Haemonchus sp. exhibiting 11% homozygous and 81% heterozygous resistance.

Conclusions: This study provides the first comprehensive evaluation of phenotypic and genotypic resistance in strongylid nematodes in Ratchaburi Province, addressing a key geographical gap in Thailand's resistance data. The findings highlight the urgent need to reassess GIN management practices and develop sustainable strategies to mitigate resistance. Furthermore, these results have significant implications for transboundary livestock health, emphasizing the necessity of collaborative efforts to combat the growing challenge to anthelmintic drugs.