Epidemiology, molecular validation and characterization of gastrointestinal nematodes in sheep: one of the first integrated epidemiological and molecular assessments of gastrointestinal nematodes in sheep from the Northwestern Himalayan region of India.

Abstract

Gastrointestinal nematode (GIN) infections remain a major constraint to sheep production, particularly in ecologically diverse mountain systems. This study presents the first comprehensive molecular epidemiological investigation of GINs infecting sheep across the Northwestern Himalayan (NWH) region of India. Between November 2022 and October 2023, faecal samples were collected from 2,500 sheep across four altitudinal zones (<&#x2009;1,000&#xa0;m to >&#x2009;3,000&#xa0;m). The overall prevalence of GIN infection was 79.4% (1,985/2,500), with significant associations observed with altitude (&#x3c7;&#xb2; = 32.64, p&#x2009;<&#x2009;0.001), age (&#x3c7;&#xb2; = 26.18, p&#x2009;<&#x2009;0.001), sex (&#x3c7;&#xb2; = 11.47, p&#x2009;=&#x2009;0.0007), and season (&#x3c7;&#xb2; = 54.92, p&#x2009;<&#x2009;0.001). Prevalence declined with increasing altitude, was highest in lambs and females, and peaked during the monsoon season. Molecular identification using ITS-2 ribosomal DNA-based PCR and sequencing confirmed the presence of five strongylid species: Haemonchus contortus, Ostertagia trifurcata, Trichostrongylus axei, Cooperia oncophora, and Nematodirus battus. Sequence analysis showed high nucleotide similarity (&#x2265;&#x2009;98-100%) with global reference isolates. Phylogenetic analysis revealed well-supported, species-specific clustering irrespective of geographic origin. These findings provide critical baseline molecular data for the NWH region and highlight the influence of altitude and seasonality on GIN transmission, supporting the development of targeted and sustainable parasite control strategies in Himalayan sheep production systems. The integration of ITS-2-based molecular diagnostics with epidemiological analysis offers a robust foundation for designing region-specific, sustainable parasite control strategies in Himalayan smallholder systems.