Molecular detection of Blastocystis in various water sources in Aegean region, Türkiye: Subtype and allele...

Blastocystis is a widely distributed anaerobic intestinal protozoan that colonizes the gastrointestinal tracts of both humans and a broad range of animal hosts. Blastocystis is transmitted predominantly via the fecal-oral route, with molecular epidemiological evidence suggesting multiple pathways, including human-to-human, zoonotic, and food- or water-borne transmission. This study investigates the presence of Blastocystis in various environmental water sources across İzmir, Türkiye, aiming to determine the subtype and allele profiles and their potential overlap with human-associated isolates. A total of 148 water samples were collected from 19 districts between 2018 and 2019, including tap, pool, well, lake, dam, stream, seawater, and thermal water sources. The presence of Blastocystis DNA in water samples was investigated using a qPCR assay. Samples with Ct ≤ 30 were further processed using conventional PCR for sequencing and subtype analysis based on GenBank and pubMLST databases. Phylogenetic trees were constructed using the Neighbor-Joining method. Blastocystis was detected in 7.43 % (11/148) of the water samples analyzed, with mean Ct values ranging from 25.02 to 33.49. Significant differences in Blastocystis positivity were observed among different types of water sources (χ² = 20.33, df = 7, p = 0.0049). A total of 148 water samples from various sources were observed, with the highest detection rate at 33.33 % (3/9; p = 0.003) in stream water, followed by 19.23 % (5/26; p = 0.012) in pool water, 11.11 % (2/18; p = 0.090) in lake water, and 9.1 % (1/31; p = 0.300) in well water. This suggests that Blastocystis positivity varies significantly depending on various water sources and that surface or stagnant waters, in particular, may serve as potential sources of contamination. Molecular analysis identified four distinct Blastocystis subtypes (ST1, ST2, ST3, and ST4), with ST3 being the most frequently detected subtype. Notably, the subtypes ST1, ST2, and ST3-previously identified in human fecal samples-were also detected in water samples from the same districts, suggesting a potential role of water sources in the transmission of Blastocystis. Therefore, regular surveillance of water sources and enhanced hygiene awareness are crucial for preventing Blastocystis transmission and safeguarding public health within the One Health framework.