Genetic diversity within dominant <italic>Enterocytozoon bieneusi</italic> genotypes in pre-weaned calves.

Background: Cattle are commonly infected with the microsporidian parasite <italic>Enterocytozoon bieneusi</italic>. Sequence characterization of <italic>E. bieneusi</italic> in these animals at the ribosomal internal transcribed spacer (ITS) locus had identified I, J and BEB4 as the dominant genotypes. However, current studies on <italic>E. bieneusi</italic> in dairy cattle are mostly on infection rates and genotype distribution. This study aims to examine the intragenotypic diversity within dominant <italic>E. bieneusi</italic> genotypes in pre-weaned dairy calves in Shanghai, China. Methods: <italic>Enterocytozoon bieneusi</italic> genotypes and subtypes were identified by PCR sequence analysis of ITS and multilocus sequence typing (MLST), based on material from farms. Chi-square test was used to examine differences in <italic>E. bieneusi</italic> infection rates between farms or age groups. Results: The overall infection rate of <italic>E. bieneusi</italic> was 26.5% (214/809), ranging from 12.6% (Farm 5) to 38.5% (Farm 4). Infection rates increased with age during early life, with the peak infection rate (43.0%; 43/100) occurring at six weeks. Four genotypes were present, including J (<italic>n</italic> = 145, 67.8%), BEB4 (<italic>n</italic> = 59, 27.6%), CHN4 (<italic>n</italic> = 4, 1.9%) and CHN15 (<italic>n</italic> = 1, 0.5%), with the former two belonging to Group 2 and the latter two belonging to Group 1. Differences were detected in the distribution of the dominant genotypes J and BEB4 among five study farms. Altogether, 10 multilocus genotypes (MLGs) were identified in the two dominant ITS genotypes, including MLG-J1 to MLG-J8 of genotype J and MLG-B1 to MLG-B2 of genotype BEB4. MLG-B1 and MLG-B2 were recovered in Farms 1, 2 and 5, whereas MLG-J1 to MLG-J5 and MLG-J6 to MLG-J8 were found in Farms 3 and 4, respectively. Conclusions: There is extensive genetic heterogeneity within the dominant <italic>E. bieneusi</italic> genotypes J and BEB4 in dairy calves in Shanghai, China, and MLST should be used in molecular epidemiological studies of <italic>E. bieneusi</italic> in cattle. [ABSTRACT FROM AUTHOR]