Evolutionary processes in populations of Cryptosporidium inferred from gp60 sequence data
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.
KeywordsDemography Expansion New Zealand Recombination Selection
The first author (JCGR) thanks the New Zealand Ministry of Health for support. mEpiLab members provided useful discussions on different stages of the study.
- Drummond AJ, et al. (2012) Geneious v.6.05. Available from http://www.geneious.com
- ESR (2017) New Zealand Public Health surveillance report, vol 15. Wellington, New ZealandGoogle Scholar
- Glaberman S, Moore JE, Lowery CJ, Chalmers RM, Sulaiman I, Elwin K (2002) Three drinking-water-associated cryptosporidiosis outbreaks, Northern Ireland. Emerg Infect Dis 8 doi:10.3201/eid0806.010368
- Guo Y, et al. (2015) Comparative genomic analysis reveals occurrence of genetic recombination in virulent Cryptosporidium hominis subtypes and telomeric gene duplications in Cryptosporidium parvum. BMC Genomics 16(320) doi:10.1186/s12864-015-1517-1
- Haldane JBS (1932) The causes of evolution. Longmans, Green & Co., LondonGoogle Scholar
- Horn B, Lopez L, Cressey P, Pirie R (2014) Annual report concerning foodborne disease in New Zealand 2013. ESR, ChristchurchGoogle Scholar
- Hudson RR (1990) Gene genealogies and the coalescent process. In: Futuyma D, Antonovics J (eds) Oxford Surveys in Evolutionary Biology, volume 7. Oxford Surveys in Evolutionary Biology, vol 7, p 1–44Google Scholar
- Maynard Smith J, Haigh J (1974) The hitch-hiking effect of a favourable gene. Cambridge University Press 23:23–35. doi:10.1017/S0016672300014634
- Strong WB, Gut J, Nelson RG (2000) Cloning and sequence analysis of a highly polymorphic Cryptosporidium parvum gene encoding a 60-kilodalton glycoprotein and characterization of its 15- and 45-kilodalton zoite surface antigen products. Infect Immun 68(7):4117–4134CrossRefPubMedPubMedCentralGoogle Scholar