Estimating the prevalence of Echinococcus spp. in a Tibetan fox (Vulpes ferrilata) population on the eastern Tibetan Plateau.

BACKGROUND: The Tibetan fox (Vulpes ferrilata) is a crucial wild definitive host of Echinococcus cestodes on the Tibetan Plateau. Fecal detection of Echinococcus DNA (fecal prevalence) is commonly used to estimate Echinococcus spp. prevalence in canine populations (population prevalence). However, this approach may be biased without individual identification, when the same individuals are repeatedly sampled, potentially leading to the misestimation of exact population prevalence. METHODS: Fecal samples collected from Tibetan foxes in Shiqu County (2010-2012) were genotyped to identify individual foxes, followed by copro-PCR to determine the population prevalence of Echinococcus spp. in the genotyped foxes. A virtual resampling program was developed to assess sampling bias and determine the optimal interval between sampling line transects. The derived optimal interval was then applied in surveillance conducted in 2015, 2016, and 2019. RESULTS: In total, 679 Tibetan fox feces were confirmed from 1219 field-collected samples (2010-2019). From 250 samples (2010-2012), 61 distinct fox individuals were identified. Virtual resampling analysis determined the optimal sampling interval to be 200-900 m, confirming fecal prevalence as an unbiased estimator of population prevalence. The implementation of a 500 m sampling interval in the surveillance of Echinococcus spp. (2010-2019) revealed an overall prevalence of 45.7% (95% CI 41.4-50.0%), with 32.3% (28.4-36.2%) for Echinococcus multilocularis and 23.5% (19.8-27.2%) for Echinococcus shiquicus. Mixed infections were detected annually, with an overall prevalence of 11.1% (8.4-13.8%). Significant temporal reductions were observed in the prevalence of E. multilocularis (Z = - 4.640, P < 0.001), mixed infections (Z = - 3.896, P < 0.001), and overall Echinococcus spp. (Z = - 2.155, P = 0.031). The prevalence trends of E. multilocularis and E. shiquicus were significantly associated, showing an inverse relationship (χ2 = 68.861, P < 0.001). CONCLUSIONS: A 200-900 m interval between feces sampling line transects was established as the optimal distance for assessing the prevalence of Echinococcus spp. in the Tibetan fox population. The persistent high prevalence of Echinococcus spp. in the Tibetan fox indicates an ongoing sylvatic transmission risk in Shiqu County. The opposing prevalence trends between E. multilocularis and E. shiquicus indicated a complex interaction within their shared host, warranting further study.