Abstract
BackgroundCryptosporidium parvum is a zoonotic pathogen worldwide. Extensive genetic diversity and complex population structures exist in C. parvum in different geographical regions and hosts. Unlike the IIa subtype family, which is responsible for most zoonotic C. parvum infections in industrialized countries, IId is identified as the dominant subtype family in farm animals, rodents and humans in China. Thus far, the population genetic characteristics of IId subtypes in calves in China are not clear.MethodsIn the present study, 46 C. parvum isolates from dairy and beef cattle in six provinces and regions in China were characterized using sequence analysis of eight genetic loci, including msc6-7, rpgr, msc6-5, dz-hrgp, chom3t, hsp70, mucin1 and gp60. They belonged to three IId subtypes in the gp60 gene, including IIdA20G1 (n = 17), IIdA19G1 (n = 24) and IIdA15G1 (n = 5). The data generated were analyzed for population genetic structures of C. parvum using DnaSP and LIAN and subpopulation structures using STRUCTURE, RAxML, Arlequin, GENALEX and Network.ResultsSeventeen multilocus genotypes were identified. The results of linkage disequilibrium analysis indicated the presence of an epidemic genetic structure in the C. parvum IId population. When isolates of various geographical areas were treated as individual subpopulations, maximum likelihood inference of phylogeny, pairwise genetic distance analysis, substructure analysis, principal components analysis and network analysis all provided evidence for geographical segregation of subpopulations in Heilongjiang, Hebei and Xinjiang. In contrast, isolates from Guangdong, Shanghai and Jiangsu were genetically similar to each other.ConclusionsData from the multilocus analysis have revealed a much higher genetic diversity of C. parvum than gp60 sequence analysis. Despite an epidemic population structure, there is an apparent geographical segregation in C. parvum subpopulations within China.
Highlights
Cryptosporidium parvum is a zoonotic pathogen worldwide
Results of the Linkage disequilibrium (LD) analysis indicate the presence of an epidemic genetic structure of C. parvum IId subtypes in the present study
This could be attributed to the high prevalence of C. parvum in calves as the result of concentrated animal feeding operations and limited number of IId subtypes in China [2]
Summary
Cryptosporidium parvum is a zoonotic pathogen worldwide. Extensive genetic diversity and complex population structures exist in C. parvum in different geographical regions and hosts. Unlike the IIa subtype family, which is responsible for most zoonotic C. parvum infections in industrialized countries, IId is identified as the dominant subtype family in farm animals, rodents and humans in China. Among the nearly 40 Cryptosporidium species identified, C. parvum is the most important species causing zoonotic cryptosporidiosis [2]. It has a wide host range, with over 20 subtype families based on. Subtyping of C. parvum in bovine studies identified an exclusive occurrence of IId subtypes in calves in China, mostly IIdA15G1 and IIdA19G1 [7]. Pre-weaned calves in industrialized countries are mostly infected with C. parvum IIa subtypes, especially IIaA15G2R1 [6, 7]
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