**5. Conclusions**

The present study was the first to analyze the community assemblage of the four protist species commonly associated with human gastrointestinal disorders in immunocompetent individuals. Our results showed the absence of any structured community between them. Their occurrence was purely random. Moreover, there was no evidence of an association between their presence and developing clinical symptomatology.

Further research, including a broad range of enteric pathogens, is needed to disentangle the complex relationships and interactions of the intestinal ecosystem. This could eventually lead to a better understanding about what are the drivers behind gastrointestinal disorders.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/pathogens10060684/s1, Table S1: Oligonucleotides and PCR conditions used for the molecular identification and/or characterization of the intestinal protist parasites investigated in Tengchong City, southwest China.

**Author Contributions:** Conceptualization, L.-G.T., D.C., C.B., and E.S.; methodology, J.-X.C.; software, C.B.; validation, J.-X.C. and L.-G.T.; formal analysis, C.B. and D.C.; investigation, Y.-H.C., Y.-F.Y. and X.-P.W.; resources, C.-L.Y.; data curation, C.-L.Y. and D.C.; writing—original draft preparation, D.C.; writing—review and editing, C.B. and S.-X.Z.; visualization, D.C.; supervision, J.-X.C.; project administration, L.-G.T.; funding acquisition, E.S. and S.-X.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the fund of the 13th Five-Year National Science and Technology Major Project for Infectious Diseases (No. 2017ZX10305501-002, No. 2018ZX10725-509), the fund of Chinese traditional medicine for treating the novel Coronavirus pneumonia patients in convalescence (No. JJ202002), the Emergency Project of Shanghai for the prevention and treatment of COVID-19 in traditional Chinese medicine (Grant No. 2020NCP001), the fund of the China Postdoctoral Science Foundation (No.2020T130022ZX), the fund of National Natural Science Foundation of China (No. 81473022). In addition, E.S. was a recipient of a Ramon y Cajal agreement (RYC-2016-21120) funded by the Spanish Ministry of Economy and Competitiveness (MINECO).

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethical Review Committee of the National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention (No. 2014004; date of approval: 12 March 2014).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** All relevant data are within the article and its additional files. The sequences obtained in this study were deposited in GenBank under accession numbers MW810321- MW810323 (*Giardia duodenalis* at the *tpi* locus) and MW798733-MW798742 (*Blastocystis* sp.).

**Acknowledgments:** We sincerely thank the efforts of the medical staff in collecting stool specimens and investigating and reporting on the subjects participating in this survey.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
