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    • The prevalence and concentration of

    2018-10-22

    The prevalence and concentration of Giardia cysts in the different locations are shown in Table 1. Sewage effluent samples showed the highest contamination with cysts (50.0%) followed by water from Nhue river (25.0%), canal water (21.7%), composted waste (20.0%), fishpond water (18.7%) and vegetables (15.3%). Significantly higher numbers of Giardia cysts were recovered in sewage effluent compared to the other water sources (p<0.05). No statistical differences in the concentration of Giardia were observed in water from the Nhue river, fishponds and canals (p>0.05). Based on ezh2 pathway analysis of the 18S rDNA gene, 23/34 samples produced amplicons of the expected size for Giardia. Sequence analysis of the 18S rDNA locus was successful for 7/23 Giardia-positive isolates; of these, six belonged to assemblage B and one to assemblage E (Table 2). Sub-typing analysis at the β-giardin locus was successfull for 5/7 Giardia isolates and these were identifed as assemblage A2 (n=2), assemblage B3 (n=2) and assemblages B1–2 (n=1) (Table 2), representing an overall result of four single contaminations with assemblage B, one single contamination with assemblage E and two mixed contaminations with assemblages A and B. The prevalence of Cryptosporidium in the different locations ranged from 15.3% to 66.7% with the highest prevalence and concentration found in sewage effluent (Table 1). The median concentrations of Cryptosporidium in sewage effluent and water from the Nhue river were significantly higher than fishpond and canal water (p<0.05). Nevertheless, no statistically significant difference was found between sewage effluent and Nhue river water samples (p=0.08). Clear and readable sequences were obtained from 9/15 amplicons and identified as C. suis (one vegetable sample and eight sewage effluent samples) (Table 2). The DNA sequence of a 587bp region of the 18S rRNA gene of these samples showed 99.8% similarity to C.suis (GU254171).
    Discussion Giardia and Cryptosporidium are highly infective, environmentally robust pathogens, insensitive to a number of disinfectants, ubiquitious in domestic and wild animals, and capable of zoonotic transmission. These factors combined, make fresh-produce and water in areas lacking adequate wastewater treatment, sanitation and proper food safety standards as primary sources of infection for humans (Slifko et al., 2000). In this study, environmental samples were sourced from a region where urban and rural practices overlap and where water and in turn vegetable quality is determined by the quality of surface water and the use of composted livestock manure and human excreta for irrigation and as agricultural fertilizer. In Vietnam, the habit of ingesting raw vegetables and herbs is common and health risks of contracting protozoan diseases are therefore likely to be associated with transmission of pathogens from contaminated irrigation water to vegetables or when workers handle the produce. High proportions of environmental contamination with both Cryptosporidium oocysts (35%) and Giardia cysts (25%) in concentrations significantly exceeding estimated infectious dosage for human (i.e. 1–100 cysts/oocysts) were recorded in the communities studied (Razzolini et al., 2011; Teunis et al., 2002). With the increased awareness of foodborne protozoan diseases, more attention should be paid to the management of food safety risks associated with protozoa in the FAO/WHO Codex Alimentarius. During recent years, several waterborne outbreaks by Giardia spp. and Cryptosporidium spp. have been documented worldwide (Baldursson and Karanis, 2011). No significant waterborne outbreaks of cryptosporidiosis and giardiosis have been reported in humans in Vietnam (Gatei et al., 2003; Ngan et al., 1992; Verle et al., 2003). Due to the highly endemic nature of both protozoa among the general population coupled with strong host immunity maintained by low-level exposure through food, water and environmental sources, the morbidity reportedly associated with these protozoa may be masked and it tends to hinder advocating the control and prevention of Giardia and Cryptosporidium (Cotruvo et al., 2004),