Patterns of Anthelmintic Resistance in Gastrointestinal Nematodes of Small Ruminants: A Systematic Review and Meta-Analysis

Abstract

Anthelmintic resistance (AHR) in gastrointestinal nematodes (GINs) threatens sustainable parasite control in small ruminants worldwide. This study estimated the global prevalence of AHR and its associated factors through a PRISMA-compliant systematic review, meta-analysis, and meta-regression registered with PROSPERO. Studies published between 1996 and March 2026 were retrieved from PubMed, Web of Science, ScienceDirect, and Google Scholar. Random-effects meta-analysis estimated the pooled prevalence of reported AHR, while subgroup and multivariable meta-regression analyses identified study-level factors associated with the prevalence of reported resistance. A total of 4809 GIN populations from small ruminant farms across 44 countries were included in the meta-analysis. The overall pooled prevalence of reported AHR was 64.6% (95% CI: 61.7–67.5), with considerable between-study heterogeneity (I2 = 77%). Benzimidazoles and macrocyclic lactones exhibited the highest prevalence of reported resistance (69.7% and 68.6%, respectively), whereas resistance to imidazothiazoles was significantly lower than that of benzimidazoles (OR = 0.66, p < 0.05). Although Haemonchus spp. was the most frequently reported resistant genus, resistance prevalence did not differ significantly among the major GIN genera. Molecular techniques were associated with significantly higher odds of detecting resistance than the faecal egg count reduction test (OR = 4.04, p < 0.05). Geographically, North America showed significantly higher resistance than Africa (OR = 1.93, p < 0.05), whereas Oceania showed significantly lower odds (OR = 0.27, p < 0.0001). The odds of reported AHR increased by approximately 9% per study year (OR = 1.09, p < 0.0001). These findings highlight the urgent need for evidence-based parasite control and standardized resistance surveillance to slow the global spread of GIN in small ruminants.