First molecular detection and subtyping of Blastocystis in pigs raised by hilly ethnic communities in Bangladesh: a zoonotic concern.

Blastocystis is a single-celled intestinal protist found worldwide in humans and animals, including pigs, and can cause gastrointestinal disorders. It can hinder pig production and pose a potential zoonotic risk. The parasite exhibits considerable genetic diversity and is currently classified into 44 recognized subtypes (STs). Of these, nine STs have been identified in pigs, eight of which are considered zoonotic. This study aimed to investigate the molecular prevalence, genetic diversity, and zoonotic potential of Blastocystis in pigs raised by the ethnic communities in the Chattogram Hill Tracts of Bangladesh. A total of 408 fresh pig fecal samples were collected from the three hill districts, Rangamati, Khagrachhari, and Bandarban, and analyzed using polymerase chain reaction (PCR) targeting the small subunit ribosomal RNA (SSU rRNA) gene. Molecular analysis revealed an overall prevalence of Blastocystis at 20.83% (85/408). Although prevalence varied across several variables, multivariable logistic regression identified location as the only significant risk factor, with pigs from Khagrachhari being almost 18 times more likely to be infected with Blastocystis compared to those from Bandarban. Among the 85 positive samples, three STs were identified: ST1, ST3, and ST5. The predominant subtype was ST5, which accounted for 92.92% of cases. Notably, all detected STs were zoonotic, underscoring the potential risk of cross-species transmission. This study presents the first report of Blastocystis infection in domestic pigs in Bangladesh and, given its high prevalence, low genetic diversity, and zoonotic potential, underscores the need for further research on its epidemiology, genetic makeup, and transmission across the country.