Enhanced detection of equine strongyles: Insights from morphological and nemabiome metabarcoding approaches in northern Iran.

Abstract

BACKGROUND: Strongyles pose significant health concerns for equids globally. Strongyles, comprising over 60 species, can lead to severe morbidity and mortality, with Strongylus vulgaris posing higher risks due to its migratory behaviour. Routine diagnostic methods, such as faecal egg counts, lack species-level resolution, while traditional morphological techniques require advanced expertise. DNA metabarcoding offers a high-throughput alternative. OBJECTIVES: To characterise the diversity of strongyles infecting horses in northern Iran and evaluate how age, sex, diagnostic methods and host population influence community composition. STUDY DESIGN: Cross-sectional. METHODS: Strongyle communities were studied across four locations. At two farms, subsets of horses were analysed either by morphological identification of adult worms or by ITS2 metabarcoding of larval cultures. Morphological identification was performed on 1476 adult worms recovered from 23 horses at two farms (Rezvanshahr and Gisum). In parallel, ITS2 nemabiome metabarcoding was applied to pools of ~2500 L3 larvae from faeces of 25 untreated horses. Community composition was analysed using dissimilarity indices (Jaccard, Bray-Curtis), PERMANOVA and generalised linear models to assess the effects of farm, method, age and sex. RESULTS: Thirty-three species were detected across both methods. DNA metabarcoding identified more species and 11 species were recorded in Iran for the first time. Strongyle community composition varied significantly among locations, including between resident and non-resident horses at the riding club, and between diagnostic methods. Neither horse age nor sex explained variation. S. vulgaris was prevalent across the majority of locations, potentially due to inconsistent treatment. MAIN LIMITATIONS: Morphological and nemabiome identifications were conducted on different subsets of horses in the same location, precluding direct within-individual comparisons. The study relied on owner-reported information about horse characteristics and management practices. CONCLUSION: These findings provide new insights into strongyle diversity in northern Iran and highlight the value of molecular diagnostics for equine parasite surveillance and control.