A new intermediate host of Echinococcus shiquicus in Qinghai-Tibet Plateau, China

Abstract

Echinococcosis is a severe parasitic zoonosis worldwide distribution, caused by the genus Echinococcus. One of its recently identified species, Echinococcus shiquicus, is believed to be endemic to the Qinghai-Tibet plateau in China. Research has confirmed that Tibetan foxes are the definitive hosts for E. shiquicus, while plateau pikas (Ochotona curzoniae) serve as intermediate hosts. In this study, cyst containing protoscolices was first observed in the lung of plateau zokor (Eospalax baileyi) in the Tibetan Autonomous Prefecture of Gannan, Gansu Province, China. This observation was confirmed using complete sequences of the cox1 and nad1 genes. We also characterized the cysts and examined the genetic diversity of Echinococcus shiquicus collected from the Qinghai-Tibet Plateau region, which includes Gansu Province, Qinghai Province, and the Tibet Autonomous Region. Phylogenetic trees and haplotype analyses for the isolates were constructed using the maximum likelihood method in MEGA 7.0.26 and DnaSP v6 software, based on the complete cox1 (1608 bp) and nad1 (897 bp) gene sequences, as well as a concatenated dataset of cox1-nad1 (2505 bp). The cyst containing protoscolices in the lung of plateau zokor was identified as Echinococcus shiquicus. The prevalence of E. shiquicus infection in plateau pikas in Luqu and Maqu counties in Gansu province was found to be 2.38% (3/126) and 3.36% (10/298), respectively, while in plateau zokors, it was 1.61% (1/62). Haplotype analysis, incorporating sequences from previous studies, revealed the presence of 17 haplotypes, indicating significant haplotype diversity in the study areas. The neutrality indices were Tajima's D = - 1.438 (P > 0.05) and Fu's Fs = - 3.169 (P > 0.05). This study provides important insights into Echinococcus shiquicus and its associations with plateau zokors and plateau pikas in the Qinghai-Tibet Plateau. We identified plateau zokors as a new natural intermediate host for E. shiquicus, emphasizing the complexity of its transmission dynamics and host interactions within this unique ecosystem. The observed morphological and developmental state differences in cysts between the liver and lung suggest that presence of tissue specificity in different organ. Additionally, the analysis of genetic diversity revealed high intraspecific variability, indicating a complex population structure influenced by various ecological factors.

Keywords: Echinococcus shiquicus; Genetic diversity; Intermediate host; Plateau zokor; Qinghai-Tibet Plateau.

Fig. 1

Map of showing the regions of investigation in this study (Tibetan Autonomous Prefecture of Gannan in Gansu Province (yellow), Haiyan County in Qinghai province (green) (Yan et al. 2021) and Damxung County in Tibet Autonomous Region (wathet) Zhu et al.

Fig. 2

The tissues of intermediate hosts were infected with Echinococcus shiquicus isolates in the Gansu province, China. E. shiquicus infection in the lung (b) of plateau zokor (a), protoscolex was observed clearly in tissue section by hematoxylin and eosin staining (c, d), E. shiquicus infection in the liver (e) and lung (g) of plateau pikas, respectively, different appearance of cysts in the liver (f) and lung (h) of plateau pikas, respectively

Fig. 3

Phylogenetic inference of Echinococcus shiquicus from Qinghai-Tibet plateau isolates (see Table 2) based on cox1 gene (a) and nad1 gene (b) and concatenated cox1-nad1 genes (c)

Fig. 4

Median-joining network of haplotypes of Echinococcus shiquicus from Qinghai-Tibet plateau isolates based on cox1 gene (a) and nad1 gene (b) and concatenated cox1-nad1 genes (c)