Associations between Schistosomiasis Intermediate Host Snail's Recent Migration Rates and Geographical Distances in Sichuan, China Open Access

Abstract

Schistosomiasis is a parasitic disease caused by several species of trematode. More than 200 million people are infected worldwide. China had made great efforts to control schistosomiasis and 60% of endemic counties had achieved interruption of Schistosoma transmission. However, the disease has reemerged in previously controlled regions in Sichuan, China. S. japonicum is the causal agent of schistosomiasis in this region. And O. hupensis snail is the sole intermediate host for S. japonicum. Understanding how environmental factors influencing O. hupensis snail migration may offer insights on strategy for in controlling schistosomiasis transmission. In this study, a Bayesian multilocus genotyping method was first used to estimate O. hupensis snail recent migration rates between populations. Mixed models were then used to assess the association between geographic distances and snail recent migration rates. Four geographic distances were modeled, namely, Euclidean distance, incline distance, stream-only distance and land-use distance. 833 O. hupensis snails from 29 villages of Sichuan province, China were sampled. The estimated median migration rate between two villages was 0.0072(IQR: 0.0034). Also 12 (2.24%) out of 536 pairwise migration rates were greater than 10%. Overall, the association between snail recent migration rates and each of the four geographical distances were very similar. All models indicate that as the geographic distances increase, snail recent migration rates decreased. There was considerable village specific heterogeneity in migration rates, which indicates that village characteristics might play an important role on snail recent migration. Further study will need to address the effect of village specific characteristics on snail recent migration. Furthermore, it will be valuable to investigate the combined effects of geographic distances, hydrological connections between villages, land-use, as well as social network on O. hupensis snail's recent migration rates.

Table of Contents

Table of Contents

Introduction. 1

Methods. 8

Data collection. 8

Recent migration rates estimation. 10

Statistical analysis. 13

Sensitivity analysis. 15

Results. 15

Descriptive analyses. 15

Modeling results. 17

Discussion. 18

Conclusion. 21

Tables. 22

Figures. 27

Supplement tables. 28

Supplement figures. 37

References. 39

APPENDIX.. 41

BAYESASS CODE. 41

About this Master's Thesis

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School	Rollins School of Public Health
Department	Biostatistics and Bioinformatics
Subfield / Discipline	Biostatistics - MPH & MSPH
Degree	MSPH
Submission	Master's Thesis
Language	English
Research Field	Biology, Biostatistics
Keyword	Schistosomiasis Geographical Distance snail recent migration
Committee Chair / Thesis Advisor	Chang, Howard, Emory University
Committee Members	Hu, Yijuan, Emory University
Partnering Agencies	Emory University schools, faculty or affiliated programs

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