High prevalence of Enterocytozoon bieneusi in asymptomatic pigs and assessment of zoonotic risk at the genotype level.

Enterocytozoon bieneusi is an emerging and clinically significant enteric parasite infecting humans and animals and can cause life-threatening diarrhea in immunocompromised people. Pigs are considered to be one of the main reservoir hosts of E. bieneusi based on their high prevalence rates and zoonotic genotypes in pigs. As an opportunistic pathogen, E. bieneusi infection of pigs can be inapparent, which leads to neglect in detecting this parasite in pigs and assessing the epidemiological role of pigs in the transmission of human microsporidiosis. In the present study, 95 healthy pigs aged 2 or 3 months were randomly selected from three areas in Heilongjiang Province, China. E. bieneusi isolates were identified and genotyped based on the small-subunit (SSU) rRNA and internal transcribed spacer (ITS) regions of the rRNA gene by PCR and sequencing. A high prevalence of E. bieneusi was observed, 83.2% (79/95) at the SSU rRNA locus versus 89.5% (85/95) at the ITS locus. Ten ITS genotypes were obtained, comprising six known genotypes—EbpA (n = 30), D (n = 19), H (n = 18), O (n = 11), CS-1 (n = 1), and LW1 (n = 1)—and four novel genotypes named HLJ-I to HLJ-IV; 70.6% (60/85) of E. bieneusi genotypes were zoonotic (genotypes EbpA, D, and O). The findings of a high prevalence of E. bieneusi in pigs and a large percentage of zoonotic genotypes indicate that pigs may play a role in the transmission of E. bieneusi to humans and may become an important source of water contamination in our investigated areas.