Even though treatment of symptomatic cases as well as improving hygiene and sanitation conditions decrease
giardiasis in underdeveloped and/or developing countries, Giardia duodenalis infection is still frequently encountered
especially in children living in crowded conditions leading to public health problems. We studied the prevalence of G.
duodenalis infection in 274 asymptomatic Thai boy orphans, living in/around the Bangkok metropolitan area, by use of
direct fecal smear and formalin-ethyl acetate techniques. This was done to explore our hypothesis that children with
asymptomatic giardiasis, who are not likely to be treated, have a high potential for spreading this pathogen. Positive
Giardia cases were further genotyped by 2 genes: small subunit ribosomal RNA (ssrRNA) and glutamate dehydrogenase
(gdh) to determine the distribution of each G. duodenalis assemblage. Positive G. duodenalis infection was 11.67 % and
revealed at 10.63%, 12% and 15%, in PK, TMK, and MHK orphanages, respectively. The overall parasitic infection,
including Giardia, was 48.54% consisting mostly of non-pathogenic organisms i.e. Blastocystis hominis, Entamoeba coli,
Endolimax nana, Entamoeba histolytica-like, Chilomastix mesnili, Trichuris trichiura, Hymenolepis nana, Strongyloides
stercoralis and Hookworm. Fourteen (70 %) and 4 (20 %) out of the 20 positive Giardia samples could be amplified by
ssrRNA and gdh genes, respectively; three belonged to the sub-assemblage BIV and only one indicated sub-assemblage
AII. Thus children infected with sub-assemblage BIV isolate are more common in this study. In conclusion, we focused
on asymptomatic giardiasis children, hitherto unrecognized, who consistently contaminate their environments with cysts.
We favor not only treating these children to eradicate the source of the infection, but also to encourage an active
surveillance program consisting of highly sensitive methods to identify silent giardiasis cases. In addition to these 2
strategies, a continuous fruitful health education program for all stakeholders is another crucial tool. These actions will
benefit the control of human giardiasis and reduce public health problems.