RESUMEN
Blastocystis hominis is a common intestinal protozoan with global distribution. The prevalence of B. hominis is extremely diverse in different countries. Molecular studies show that there is a great deal of genetic variation in the Blastocystis parasite isolated from humans and animals. Therefore, this study was conducted to determine B. hominis genotypes in patients attending to health centers of Sari, Mazandaran Province, north of Iran. 420 fecal specimens were collected from individuals in health centers of Sari from April to December 2017. The samples were examined by direct methods, parasite test (formalin ether) and Giemsa staining. In order to determine the genotypes of Blastocystis parasite, all positive samples in direct methods were tested by PCR using SSU rDNA gene. Eventually, seven positive molecular samples were sequenced and recorded in the gene bank. The phylogenetic analysis was done by drawing a gene tree using the neighbor-joining procedure. B. hominis was detected in 60 stool specimens by microscopic method. All these 60 samples were positive by PCR and the bands 310 bp were observed. According to the phylogenetic tree, it was revealed that B. hominis isolates of Mazandaran Province are more similar to subtype ST3 (ST type) that reported in Khorramabad in Lorestan Province (West of Iran). The present study showed that, like most studies, ST3 is the dominant genotype of protozoan in Sari. Improvement of public health awareness, relative improvement in environmental health, urban wastewater treatment, proper clothing coverage and the use of gloves during dealing with livestock and the use of domestic water treatment devices can reduce the Blastocystis infection in this area.