Blastocystis One Health Approach in a Rural Community of Northern Thailand: Prevalence, Subtypes and Novel Transmission Routes

Abstract

Blastocystis is the most commonly found eukaryote in the gut of humans and other animals. This protist is extremely heterogeneous genetically and is classified into 28 subtypes (STs) based on the small subunit ribosomal RNA (SSU rRNA) gene. Numerous studies exist on prevalence of the organism, which usually focus on either humans or animals or the environment, while only a handful investigates all three sources simultaneously. Consequently, understanding of Blastocystis transmission dynamics remains inadequate. Our aim was to explore Blastocystis under the One Health perspective using a rural community in northern Thailand as our study area. We surveyed human, other animal and environmental samples using both morphological and molecular approaches. Prevalence rates of Blastocystis were 73% in human hosts (n = 45), 100% in non-human hosts (n = 44) and 91% in environmental samples (n = 35). Overall, ten subtypes were identified (ST1, ST2, ST3, ST4 ST5, ST6, ST7, ST10, ST23, and ST26), eight of which were detected in humans (ST1, ST2, ST3, ST4, ST5, ST7, ST10, and ST23), three in other animals (ST6, ST7, and ST23), while seven (ST1, ST3, ST6, ST7, ST10, ST23, and ST26) were found in the environment. In our investigation of transmission dynamics, we assessed various groupings both at the household and community level. Given the overall high prevalence rate, transmission amongst humans and between animals and humans are not as frequent as expected with only two subtypes being shared. This raises questions on the role of the environment on transmission of Blastocystis. Water and soil comprise the main reservoirs of the various subtypes in this community. Five subtypes are shared between humans and the environment, while three overlap between the latter and animal hosts. We propose soil as a novel route of transmission, which should be considered in future investigations. This study provides a thorough One Health perspective on Blastocystis. Using this type of approach advances our understanding on occurrence, diversity, ecology and transmission dynamics of this poorly understood, yet frequent gut resident.

Subtypes and phylogenetic analysis of Blastocystis sp. isolates from West Ismailia, Egypt

“…transmission is not clearly defined, but a human transmission cycle has been proposed [17][18][19] . Nonetheless, studies of family units in developed and developing countries have indicated that this pathway remains to be conclusively demonstrated 20,21 . Additional sources of infections appear to be contaminated water [22][23][24][25] , close contact with animals 1 , and contaminated soil 20 .…”

High resistance of Blastocystis to chlorine and hydrogen peroxide

“…Water is a common vehicle for transmission of many pathogenic and non-pathogenic organisms, including Blastocystis (Jinatham et al 2021(Jinatham et al , 2022. Chlorine is one of the most widely used reagents for water disinfection.…”

“…Blastocystis exhibits remarkable genetic diversity and at least 28 subtypes (STs, ST1-ST17, ST21, ST23-32) -arguably species -have been identi ed in humans, other mammals and birds, based on genetic heterogeneity across the small subunit rRNA (SSU rRNA) gene (Maloney et al 2020; Stensvold and Clark 2020; Higuera et al 2021). Of these subtypes, ST1-ST9, ST10, ST12, ST14, ST16 and ST23 have been found in humans, with ST1-ST3 being the three most prevalent and globally distributed (Yoshikawa et al 2004;Meloni et al 2011;Forsell et al 2012;Khaled et al 2020;Jinatham et al 2021;Osorio-pulgarin et al 2021). However, these subtypes have also been found in several other hosts, indicating the lack of host speci city of Blastocystis (Stensvold and Clark 2016), at least at subtype level.…”

Resistance of Blastocystis to chlorine and hydrogen peroxide

“…Blastocystis exhibits remarkable genetic diversity, and at least 28 subtypes (STs, ST1-ST17, ST21, ST23-32) -arguably species -have been identified in humans, other mammals, and birds, based on genetic heterogeneity across the small subunit rRNA (SSU rRNA) gene (Maloney et al 2020;Stensvold and Clark 2020;Higuera et al 2021). Of these subtypes, ST1-ST9, ST10, ST12, ST14, ST16, and ST23 have been found in humans, with ST1-ST3 being the three most prevalent and globally distributed (Yoshikawa et al 2004;Meloni et al 2011;Forsell et al 2012;Khaled et al 2020;Jinatham et al 2021;Osorio-pulgarin et al 2021). However, these subtypes have also been found in several other hosts, indicating the lack of host specificity of Blastocystis (Stensvold and Clark 2016), at least at subtype level.…”

“…Links to irritable bowel syndrome and inflammatory bowel disease have also been postulated though not conclusively established (Domínguezmárquez et al 2009;Roberts et al 2013;Salvador et al 2016;Peña et al 2020;Shirvani et al 2020). However, Blastocystis is also very common in the gut of people with no gastrointestinal symptoms (Nagel et al 2012;Scanlan et al 2015;Yowang et al 2018;Jinatham et al 2021). Hence, it is possible that Blastocystis colonization in general is not harmful, but rather specific subtypes or strains within subtypes might be the ones potentially causing symptomology.…”