Epidemiology of Eustrongylides sp. Infection in Triplophysa strauchii: Temporal Dynamics and Risk Factors

The epidemiology of the nematode Eustrongylides sp. remains poorly understood in natural fish populations, especially under alpine conditions. This study investigated its infection dynamics in Triplophysa strauchii, an endemic fish in an alpine wetland in northwestern China. A total of 720 fish were sampled monthly from April to November 2025. Parasitic larvae were identified using ribosomal ITS sequences. Hurdle models were employed to assess infection risk and intensity, incorporating host length, sex, and month as predictors. The overall prevalence was 21.8%, with a mean intensity of 4.36 ± 6.83 worms per infected fish. Infection dynamics showed two seasonal peaks: a spring peak with high intensity and a late-summer peak with moderate prevalence but low intensity. Host length was the most stable predictor for both infection risk (OR = 1.916 per cm, 95% CI: 1.232–2.977) and intensity, with significant length × month interactions (length × May: IRR = 4.847, p = 0.005; length × November: OR = 0.418, p = 0.005), indicating seasonal modulation of the length effect. These findings provide foundational insights into parasite transmission in alpine wetlands and highlight public health concerns regarding fish consumption.