Background: The schizothoracine fishes, an excellent model for several studies, is a dominant fish group of the Qinghai-Tibet Plateau (QTP). However, species populations have rapidly declined due to various factors, and infection with Echinorhynchus gymnocyprii is cited as a possible factor. In the present study, the molecular characteristics of E. gymnocyprii in four species of schizothoracine fishes from the QTP were explored. Methods: We investigated the infection status of E. gymnocyprii in 156 schizothoracine fishes from the upper Yangtze River, upper Yellow River, and Qinghai Lake in Qinghai Province, China. The complete internal transcribed spacer (ITS) of the ribosomal RNA (rRNA) gene and part of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene of 35 E. gymnocyprii isolates from these fishes were sequenced and their characteristics analyzed. In addition, we inferred phylogenetic relationships of the E. gymnocyprii populations based on the rRNA-ITS and cox1 sequences. Results: The total prevalence of E. gymnocyprii in schizothoracine fishes was 57.69% (90/156). However, the prevalence among different species as well as that across the geographical locations of the schizothoracine fishes was significantly different. The results of sequence analysis showed that the four E. gymnocyprii populations from different hosts and regions of Qinghai Province were conspecific, exhibiting rich genetic diversity. Phylogenetic analysis based on rRNA-ITS and cox1 sequences supported the coalescence of branches within E. gymnocyprii; the cox1 gene of E. gymnocyprii populations inferred some geographical associations with water systems. In addition, three species of schizothoracine fishes were recorded as new definitive hosts for E. gymnocyprii. Conclusions: To the best of our knowledge, this is the first molecular description of E. gymnocyprii populations in schizothoracine fishes from the Qinghai-Tibet Plateau that provides basic data for epidemiological surveillance and control of acanthocephaliasis to protect endemic fish stocks.

The objective of this investigation was to understand the epidemiology of fascioliasis in yaks in the alpine pastoral areas of the Qinghai–Tibet Plateau, China. The prevalence of Fasciola hepatica infection was estimated by examining eggs in the feces of yaks and by autopsy after the slaughter. Yaks were sampled from a total of 16 representative counties in Qinghai province, and risk factors were assessed based on regional and age characteristics. Fecal samples were obtained from 1542 yaks aged 0–1 (<1 year old), 1–2 (≥1 year old and <3 years old), and over 3 years (≥3 years old). In addition, 242 yaks over 3 years old who had not undergone fecal examinations were randomly selected for autopsy. A total of 267 fecal samples were positive for Fasciola spp. eggs. The average infection rate was 17.32% (0–60.61%), and the average infection intensity was 51.9 eggs per gram (epg) of feces, with intensities ranging from 18 to 112 epg. In Maduo, Dari, Zhiduo, Chengduo, and Datong counties, the Fasciola spp. eggs infection rate was zero. Fasciola spp. adult flukes were detected in 66 out of 242 yaks at autopsy, with a total infection rate of 27.27% and an average infection intensity of 21.2 (adult worms), with intensities ranging from 3 to 46 worms. Logistic regression model analysis showed that age was a significant risk factor for yak infection with Fasciola spp. In addition, the risk varied between regions: Haiyan, Gangcha, Duran, and Wulan were all high-risk areas for yak infection with Fasciola spp. The spatial distribution of the Fasciola spp. infection rate in each region showed a very weak negative correlation (Moran’s I = −0.062), Duran formed a spatial distribution of high–low clusters with surrounding areas, and Datong formed a low–high clustering distribution characteristic with the surrounding areas. This investigation revealed that the infection rate of Fasciola spp. in yaks was higher on the Qinghai–Tibet Plateau. Increasing age was a risk factor for infection with Fasciola spp.; different regions also have a different risk of Fasciola spp. infection. Only two regions showed clustering characteristics in the spatial distribution of infection rates. These findings extend the epidemiological information on Fasciola spp. infection in yaks and provide baseline data for the execution of control measures against Fasciola spp. infection.