Molecular identification and subtypes analysis of Blastocystis in South Khorasan province, Eastern Iran

Background: Blastocystis is a prevalent intestinal parasitic protist that infects both birds and animals. There are at least 44 subtypes (ST) of Blastocystis, with ST1-ST9 being found in humans. The correlation between specific subtypes and pathogenicity has not been definitively established. This study aimed to identify the genetic diversity within subtypes of Blastocystis in stool samples collected from individuals who were referred to medical facilities in the cities of Birjand, Darmian, Nehbandan and Ferdows, Eastern Iran.

Methods: A total of 1800 stool specimens were randomly collected from referred individuals in selected medical laboratories of South Khorasan province. DNA was extracted and PCR before, sequencing and subtyping were performed for characterization and phylogenetic analysis.

Results: A total of 118 (6.5%) individuals were examined positive with Blastocystis through microscopic observations. A ~ 620-bp segment of the SSU rRNA gene of Blastocystis was amplified and were genetically evaluated using MEGA6 and DnaSP. 30 samples of Blastocystis positive samples were sequenced. BLAST analyses identified 3 distinct subtypes including ST1 (11, 36.66%), ST2 (5, 16.68%), ST3 (14, 46.66) within our samples. Intra-subtype discrimination showed the similarity of 95.88%, 91.56% and 92.14% for ST1 and ST2, ST1 and ST3, and ST2 and ST3, respectively. Additionally, allele 4 for ST1; allele 12 for ST2; and alleles 34 and 36 for ST3 were detected.

Conclusions: As results, ST1 exhibited the highest nucleotide diversity (π: 0.00113), suggesting a high degree of genetic diversity within this subtype. Phylogenetic analysis showed that, ST3 was clustered to animal isolates from cattle and cats, indicating the potential zoonotic transmission of Blastocystis.