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Evolutionary processes in populations of Cryptosporidium inferred from gp60 sequence data

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Abstract

Cryptosporidiosis is one of the most common human infectious diseases globally. The gp60 gene has been adopted as a key marker for molecular epidemiological investigations into this protozoan disease because of the capability to characterize genotypes and detect variants within Cryptosporidium species infecting humans. However, we know relatively little about the potential spatial and temporal variation in population demography that can be inferred from this gene beyond that it is recognized to be under selective pressure. Here, we analyzed the genetic variation in time and space within two putative populations of Cryptosporidium in New Zealand to infer the processes behind the patterns of sequence polymorphism. Analyses using Tajima’s D, Fu, and Li’s D* and F* tests show significant departures from neutrality in some populations and indicate the selective maintenance of alleles within some populations. Demographic analyses showed distortions in the pattern of the genetic variability caused by high recombination rates and population expansion, which was observed in case notification data. Our results showed that processes acting on populations that have similar effects can be distinguished from one another and multiple processes can be detected acting at the same time. These results are significant for prediction of the parasite dynamics and potential mechanisms of long-term changes in the risk of cryptosporidiosis in humans.

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Acknowledgments

The first author (JCGR) thanks the New Zealand Ministry of Health for support. mEpiLab members provided useful discussions on different stages of the study.

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Correspondence to Juan C. Garcia-R.

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Table S1

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Figure S1

Mismatch distribution analyses showing the frequencies of pairwise differences of C. hominis in Auckland 2012 (A), Auckland 2013 (B), Auckland 2014 (C), Auckland 2015 (D), and Canterbury 2014 (E). The observed distributions (red dotted line) are compared to the expected distribution (black solid line) under a model of sudden expansion. X-axis: number of pairwise differences, Y-axis: frequency. (JPEG 3507 kb)

Figure S2

Mismatch distribution analyses showing the frequencies of pairwise differences of C. parvum in Auckland 2010 (A), Auckland 2011 (B), Auckland 2012 (C), Auckland 2013 (D), Auckland 2014 (E), Auckland 2015 (F), Canterbury 2010 (G), Canterbury 2013 (H), Canterbury 2014 (I) and Canterbury 2015 (J). The observed distributions (red dotted line) are compared to the expected distribution (black solid line) under a model of sudden expansion. X-axis: number of pairwise differences, Y-axis: frequency. (JPEG 5661 kb)

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Appendix 1

Appendix 1

Alignments of gp60 sequences from the populations used in this study. Files are in nexus format with blocks of information containing the number of individuals per year of C. hominis in Auckland (Dataset 1), C. hominis in Canterbury (Dataset 2), C. parvum in Auckland (Dataset 3) and C. parvum in Canterbury (Dataset 4).

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Garcia-R, J.C., Hayman, D.T.S. Evolutionary processes in populations of Cryptosporidium inferred from gp60 sequence data. Parasitol Res 116, 1855–1861 (2017). https://doi.org/10.1007/s00436-017-5459-1

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  • DOI: https://doi.org/10.1007/s00436-017-5459-1

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