High genetic diversity of Giardia duodenalis assemblage E in Chinese dairy cattle.

Giardia duodenalis is a common protozoan parasite that can infect humans and animals. Although previous studies demonstrated that the assemblage E of G. duodenalis is prevalent in cattle, studies on its genetic diversity were mostly based on single loci and very few involved multilocus analysis. To better understand the genetic variability and structure of G. duodenalis assemblage E in Chinese dairy cattle, 651 multilocus sequences derived from nine provinces (Gansu, Guangdong, Henan, Jiangsu, Ningxia, Shaanxi, Shanghai, Sichuan and Xinjiang) of China were analyzed in this study. Results showed that a total of 220 haplotypes were identified in the G. duodenalis assemblage E, with a high haplotype diversity (Hd = 0.97225) and low nucleotide diversity (π = 0.00259). The genetic differentiation index (FST) and gene flow (Nm) results indicated low degree of genetic differentiation, implying frequent genetic communication. Combined with the analysis of molecular variance (AMOVA), genetic variation within populations (81.7%) was higher than that among populations (18.3%), indicating low degree of genetic differentiation between populations. Such low rates of gene differentiation supported no significant correlations with geographical divisions. Moreover, both negative Tajima's D and Fu's FS values of neutrality tests and unimodal curve of mismatch distribution analyses indicated that G. duodenalis assemblage E population in Chinese dairy cattle had experienced demographic expansion. Overall, these findings contribute to an improved understanding of the population genetics and evolutionary biology of G. duodenalis assemblage E and assist in its control in cattle.