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Abstract The Orang Asli (OA), Malaysia’s indigenous minority, continue to experience ongoing soil-transmitted helminth (STH) infections despite efforts including the Resettlement Programme (RPS). This study explores STH epidemiology and associated risks of moderate-to-heavy infections among 259 indigenous Negritos across four states in Peninsular Malaysia. Stool samples, anthropometrics, haemoglobin levels (finger-prick) and sociodemographic and environmental-sanitation factors via pretested questionnaires were collected. Parasitological examinations (direct faecal smear, formol-ether concentration, and Kato-Katz techniques) were thoroughly performed. The study revealed a 63.3% overall STH prevalence, with Trichuris trichiura (57.9%) being the most common, followed by Ascaris lumbricoides (35.5%) and hookworm (8.9%). Moderate-to-heavy infections were observed in 39.3% for T. trichiura and 48.9% for A. lumbricoides, with mixed infections of these two species being the most prevalent (50.6%). The risk for moderate-to-heavy infection increased significantly if other household members were infected (P

In indigenous populations where soil-transmitted helminths (STH) infections are endemic, STH parasites (i.e., Ascaris lumbricoides, Trichuris trichiura, hookworms) often co-exist and co-evolve with the gut microbiota of their human hosts. The association between STH infections and the gut microbiota of the colonized human hosts has been established, but few studies explored the gut microbiota of the parasites. This preliminary study aimed to characterize the microbiota of the STH parasite for further understanding the STH parasite-host relationship. The gut microbial genomic DNA from four adult A. lumbricoides worms recovered from a six-year-old indigenous Negrito boy living in an STH-endemic village in Perak, Peninsular Malaysia was extracted and sequenced for the V3-V4 region of the 16S rRNA. The microbiota profiles of these worms were characterized and compared with the gut microbiota of their human host, including the profiles from four STH-positive and three STH-negative individuals from the same tribe and village. The gut microbial structure of A. lumbricoides was found to be differed significantly from their human host. The worms contained lower gut bacterial abundance and diversity than human. This difference was evident in the beta diversity analysis which showed a clear separation between the two sample types. While both Firmicutes (52.3%) and Bacteroidetes (36.6%) are the predominant phyla followed by Proteobacteria (7.2%) in the human gut, the microbiota of Ascaris gut is highly dominated by Firmicutes, constituting 84.2% relative abundance (mainly from the genus Clostridium), followed by Proteobacteria (11.1%), Tenericutes (1.8%) and Bacteroidetes (1.5%). The parasites were also found to alter the microbial structure of the human gut following infection based on the relatively higher bacterial abundance in STH-positive versus STH-negative participants. Further studies with a greater number of Ascaris adults and human hosts are needed to confirm the gut microbiota profiles.