Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 9 1 2014 03 15 70 78 EN Mohammad Rayani Department of Microbiology and Parasitology, School of Health, Bushehr University of Medical Sciences, Bushehr, Iran AND Department of Medical Microbiology and Parasitology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Malaysia. Ngah Zasmy UNYAH Department of Medical Microbiology and Parasitology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Malaysia. Gholamreza Hatam Basic Sciences in Infectious Diseases Research Center, Medical School, Shiraz University of Medical Sciences, Shiraz, Iran. 2015 10 14 Background: Giardia duodenalis is one of the most common human intestinal pro-tozoan parasites worldwide and is endemic throughout the world with a vast range of mammalian hosts. The present study aimed to identify the prevalence of G. duo-denalis isolates and determine the most common of its assemblages in the patients referring to health centers and hospitals in Fars province, Iran that will be subjected to further molecular investigation. Methods: We collected 1000 human fecal samples from health centers and hospi-tals in Shiraz, Iran in a one year period from September 2009 to August 2010. Mi-croscopic examination for the presence of G. duodenalis cysts and trophozoites was performed by direct wet mount before and after the concentration techniques. Ex-traction of DNA was performed by Phenol-Chloroform-Isoamylalcohol (PCI). G. duodenalis-positive specimens were analyzed by PCR. A fragment of the SSU-rDNA (292 bp) gene was amplified by PCR using the forward primer RH11 and the re-verse primer RH4. Genotyping was performed using sequence analysis of G. duode-nalis glutamate dehydrogenase gene using primers GDHeF, GDHiF, and GDHiR. Results: The prevalence of Giardia infection was 10.7% (107/1000) examined based on microscopic examination. PCR identified 80% (40/50) of the samples as positive for G. duodenalis based on SSU-rDNA amplification on sucrose gradient samples. Besides, genotyping results indicated 32 isolates (80%) as assemblage AII and 8 isolates (20%) as assemblage BIII and BIV based on the DNA sequence analysis of the glutamate dehydrogenase locus of G. duodenalis. Conclusion: The findings of this study emphasize that Iran (Fars Province) is a favorable area for giardiasis with an anthroponotic infection route. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/431 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/431/307