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

Abstract

Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.