| The parasitic protozoa Giardia is a genus of intestinal flagellates that infects a wide range of hosts throughout the world. Giardia can cause diarrhoea diseases in many vertebrate hosts, including humans. Transmission of the Giardia duodenalis cysts to humans occurs by fecal oral route transmission, either by direct contact or by ingestion of contaminated food or water. Since 1970s, the sporadic cases or epidemic outbreak of giardiosis have been reported in the world. The giardiosis has been listed into one of the 10 most major parasitic diseases worldwide. The object of this study is to understand the prevalence status of Giardia duodenalis in humans in partial areas in Henan Province, and genetically characterize the G. duodenalis-positive isolates obtained in investigation,thus to gain a better analyzing the infection source of human giardiosis.Between 2007 and 2008, an epidemiological investigation was performed in Linzhou (0-15 years children), inpatients in the people's hospital of Henan province, and two hoapitals in Kaifeng city. A total of 7519 fecal samples were examined by microscope of iodine wet mount smears. 23 samples were Giardia-positive, thus the overall infection rate was 0.31% (23/7519).The infection rate for persons aged 7-10 years old was 1.28% (5/392), 0.46% (10/2190) for persons aged 1-6 years. The prevalence for persons aged 10-20, 21-40, 41-60 and > 60 years old was 0%, 0.34%, 0.11%, 0.13%, respectively. There was a significant difference prevalence of Giardia in the different age groups, with a more frequent occurrence in 7-10 years children (P < 0.01). The infection rate for female and male persons was 0.25% (14/3932) and 0.36% (9/3587), respectively. No significant difference of prevalence was observed between men and women (P > 0.05).According to the TPI gene sequences of Giardia spp. doposited in GenBank, a set of primers were designed and used to amplify the Giadia isolates by nested-PCR. The anneal temperature was optimized, then a about 530bp fragment was successfully amplified. In contrast, the other three DNA samples from three species of parsites were not showed the aim amplicon. The results indicated that the primers designed were very special to amplify Giardia spp. Therefore, the present established nested-PCR method can been used in the molecular epidemiological survey.23 Giardia-positive samples were amplified by the established method, 20 samples were successfully amplified. Then 18 from the 20 PCR products were successfully sequenced. Sequence alignment analysis showed the 18 isolates belonged to two assemblages, including 12 assemblage A and 6 assemblage B. Subtype analysis indicated 8 were A-I and four had A-II among the 12 assemblage A. In contrast, the six assemblage B represented six new subtypes, named as B1-B6. Phylogenetic analysis further confirmed the results of alignment analysis. In the pelogenetic tree, 18 isolates consisted of two clades, one clade was assemblage A and the other clade belonged to assemblage B. Moreover, 8 A-I isolates and 4 A-II isolates occupied two different taxons. The present data suggest the A-I subtype was the predominant subtyes in assemblage A, whereas this observation was different from that seen in oher countries. In addition, among the three areas, the isolates were all assemblage A and had more A-I subtype in Linzhou, Kaifeng had more assemblage B than the other two areas, whereas the distribution of assemblages or subtyes were more complexed in Zhengzhou. This findings possibly indicate that there is a different distribution of geotypes or subtypes of Giardia duodenalis in different areas.
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