Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 21 2 2026 07 12 258 264 Samaneh Boulaghi Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Amirali Reihani 1. Student Research Committee, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran 2. Health Policy Research Center, Institute of Health, Shiraz University of Medical Sciences, Shiraz, Iran BiBi Razieh Hosseini Farash 1. Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran 2. Cutaneous Leishmaniasis Research Center, Mashhad University of Medical Sciences, Mashhad, Iran Yousef Sharifi Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Omid Ahmadi 4. Cutaneous Leishmaniasis Research Center, Mashhad University of Medical Sciences, Mashhad, Iran 2. Department of Parasitology and Mycology, Torbat Jam Faculty of Medical Sciences, Torbat Jam, Iran Alireza Samadi Department of Cell and Molecular Biology, Faculty of Life Sciences and Biotechnology, Shahid Beheshti University, Tehran, Iran Ghodratollah Salehi Sangani Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Mohsen Najjari Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Fariba Berenji Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Mehdi Zarean 1. Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran 2. Cutaneous Leishmaniasis Research Center, Mashhad University of Medical Sciences, Mashhad, Iran 2025 12 06 2026 07 12 Background: Blastocystis spp. is a globally distributed intestinal protozoan that infects humans and various animals. This protozoan is a common pathogen among humans and animals and can be transmitted from animal species to humans. Therefore, the present study aimed to identify and characterize Blastocystis subtypes in children with gastrointestinal symptoms using PCR and sequencing. Methods: Overall, 150 stool samples were collected from children referred to academic hospitals in Mashhad, Iran over a period of seven months in 2020. Participants were divided into two groups: symptomatic cases (n = 50) and asymptomatic controls (n = 100). DNA was extracted from Blastocystis-positive samples and analyzed by PCR followed by sequencing for subtype identification. Results: Blastocystis spp. was found in 6 (12%) of the symptomatic children and 7 (7%) of the asymptomatic group. All isolates from symptomatic cases belonged to subtype ST1, whereas isolates from the control group included ST1, ST2, ST3, and ST7. ST1 was the most frequently detected subtype overall. Among symptomatic children, abdominal pain was the most frequent symptom. Conclusion: ST1 was the predominant subtype in both symptomatic and asymptomatic children, though it was the only subtype observed in symptomatic cases. These findings suggest a potential link between ST1 and gastrointestinal symptoms. Further studies with larger populations and in diverse geographic regions are warranted to investigate the clinical significance and distribution patterns of Blastocystis subtypes. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/4835 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/4835/1500