Multiscale epidemiology of gastrointestinal nematode infections in small ruminants: field evidence from Inner Mongolia and a national meta-analysis in China

Gastrointestinal nematodes (GINs) are among the most important parasites constraining small-ruminant production. However, epidemiological evidence in China remains fragmented because existing studies differ substantially in geographic coverage, host species, sampling periods, diagnostic approaches, and ecological settings. We applied a multiscale framework integrating a regional survey in Inner Mongolia with a national systematic review and meta-analysis. In the regional survey, 2,084 fecal samples were collected from sheep aged 6–12 months in Ulanqab, Alxa, and Ordos from August 2020 to September 2021 and examined using a modified McMaster method. Detected eggs were classified into broad morphologic categories. For the national analysis, six databases were searched following PRISMA guidelines, and eligible cross-sectional studies were synthesized using random-effects models. The regional survey showed an overall GIN prevalence of 28.8% (601/2,084), with marked spatial variation among Ordos (74.0%), Ulanqab (53.2%), and Alxa (11.9%). Strongyle-type and Nematodirus -type eggs were detected in 25.3% and 17.5% of samples, respectively, with co-positivity in 14.0%. Nationally, 50 studies comprising 53,955 small ruminants were included. The random-effects pooled prevalence was 71% (95% CI: 64%–78%), with extreme heterogeneity (I² = 100%). Marshallagia and Haemonchus showed relatively high pooled estimates among reported taxa, while subgroup differences by host species, age, and feeding system were not statistically significant. The findings demonstrate marked local variation in GIN prevalence in the regional survey and substantial descriptive spatial variation across the provincial-level estimates included in the national meta-analysis. The regional microscopy-based survey supports broad egg-category inference but not reliable genus- or species-level identification of non- Nematodirus strongylid nematodes. These results support geographically targeted surveillance and locally adapted parasite-control strategies, while national pooled and subgroup estimates should be interpreted cautiously because of marked heterogeneity.