Molecular Epidemiology of Human Cryptosporidiosis
Most human cryptosporidiosis is caused by the species Cryptosporidium hominis and C. parvum, with less common species globally including C. meleagridis, C. cuniculus, C. ubiquitum, C. viatorum, C. canis and C. felis, although the distribution and prevalen
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Molecular Epidemiology of Human Cryptosporidiosis Gordon L. Nichols, Rachel M. Chalmers, and Stephen J. Hadfield
Abstract Most human cryptosporidiosis is caused by the species Cryptosporidium hominis and C. parvum, with less common species globally including C. meleagridis, C. cuniculus, C. ubiquitum, C. viatorum, C. canis and C. felis, although the distribution and prevalence may vary. Minor species that are only very rarely found in symptomatic people include C. andersoni, C. suis, C. scrofarum, C. bovis, and C. muris. The use of molecular methods to characterise isolates has contributed to our understanding of the overall epidemiology of cryptosporidiosis and its transmission, the biology and host range of each species and the evolution from a common ancestor. The development of more discriminatory typing methods has shown that outbreaks may be caused by subtypes identified at particular loci. The 60 kDa glycoprotein (gp60) gene has been the most widely used locus due to its high sequence variation. A gp60 naming system has been proposed and widely adopted which has greatly assisted with global epidemiological analysis. However, limitations of a single locus scheme have been identified including low gp60 subtype diversity in certain countries. A plethora of multilocus genotyping (MLG) methods have been developed to provide increased discrimination and are beginning to deepen our understanding of parasite population structures and transmission dynamics. However, there is a need for a standard MLG scheme that, when applied to routine surveillance datasets, will distinguish between outbreak and sporadic cases. This will allow investigation of geographically and temporally dispersed outbreaks which is not currently possible in areas of low gp60 sequence variation. G.L. Nichols (*) European Centre for Disease Prevention and Control, Tomtebodava¨gen 11A, Stockholm, Solna 17183, Sweden University of East Anglia, University of Thessaly, Public Health, England e-mail: [email protected] R.M. Chalmers • S.J. Hadfield Cryptosporidium Reference Unit, Public Health Wales Microbiology, Singleton Hospital, Swansea SA2 8QA, UK e-mail: [email protected]; [email protected] S.M. Caccio` and G. Widmer (eds.), Cryptosporidium: parasite and disease, DOI 10.1007/978-3-7091-1562-6_3, © Springer-Verlag Wien 2014
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Introduction to Molecular Epidemiology
Cryptosporidiosis is a disease that can be controlled by interventions; these are currently directed at limiting exposure to the parasite. Although vaccination has been attempted (Roche et al. 2013) there are no commercial vaccines and specific treatment options are limited (McDonald 2011). In order to intervene and prevent disease, epidemiological investigations should focus on identifying those at most risk, determining sources, transmission pathways, hosts and vectors and risk factors that are linked with infection. The evidence to date suggests clear human and animal sources and transmission routes that commonly inv
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