Molecular Epidemiology and Genotyping of Blastocystis sp. Among Patients in Guilan, Northern Iran

Background: Blastocystis sp. is an anaerobic intestinal protozoan with extensive genetic diversity and controversial pathogenicity. The distribution and molecular subtypes of this entity in Guilan province, northern Iran, remain under-investigated. Objective: This study aimed to determine the prevalence and molecular subtypes of Blastocystis sp. in Rasht, Guilan Province, Iran. Methods: In this cross-sectional study (2023–2024), 300 stool samples were collected from patients referred to the medical laboratory at Razi Hospital. Microscopic examination and PCR amplification targeting the SSU rDNA gene were performed. Sequencing was performed on the positive isolates, and subtyping was achieved through BLAST alignment and subsequent phylogenetic analysis. Results: The overall prevalence of Blastocystis sp. was 12.3% (n = 37). No significant associations were found between infection and age, sex, or place of residence (p > 0.05). Molecular characterisation (23.08%). No statistically significant correlation was observed between subtypes and clinical symptoms, although ST1 and ST7 were more frequently detected in symptomatic individuals. Conclusions: Blastocystis sp. showed notable subtype diversity in the studied population, including the potentially zoonotic ST7. However, no significant association was found between subtypes and clinical manifestations. These findings support sustained molecular epidemiological surveillance and larger-scale studies to clarify subtype-specific pathogenesis and transmission dynamics.