Prevalence and Molecular Subtype Distribution of Blastocystis sp. in Commercial Crossbred Pigs and Tibetan Pigs in Yunnan Province, China: A Cross-Sectional Study

Blastocystis sp. is a common intestinal protist colonizing humans and a wide range of animals, and pigs are considered an important animal host for several subtypes with potential zoonotic relevance. Although porcine Blastocystis has previously been investigated in Yunnan Province, contemporary information on its geographic and seasonal variation and regional subtype composition remains limited. In this cross-sectional study, 946 fecal samples were collected from commercial crossbred pigs and Tibetan pigs in six regions of Yunnan Province between April 2023 and December 2024. PCR and sequencing revealed the prevalence and genetic subtypes. The overall Blastocystis sp. prevalence was 39.43% (373/946, 95% CI: 36.31–42.55%). Pearson’s chi-square tests showed significant differences among geographic regions (χ2 = 107.18, p < 0.001), seasons (χ2 = 51.85, p < 0.001), and age groups (χ2 = 14.81, p < 0.001). Regarding the regions, the prevalence in Pu’er, Honghe, Zhaotong, Diqing, Chuxiong, and Baoshan was 68.75% (66/96; 95% CI: 59.31–78.19%), 63.43% (85/134; 95% CI: 55.17–71.69%), 35.98% (127/353; 95% CI: 30.95–41.01%), 35.17% (51/145; 95% CI: 27.31–43.04%), 23.53% (40/170; 95% CI: 17.09–29.97%), and 8.33% (4/48; 95% CI: 0.22–16.44%), respectively. In terms of age, pigs aged >6 months had a significantly higher prevalence of 42.65% (316/741; 95% CI: 39.08–46.21%) than pigs aged ≤6 months 27.80% (57/205; 95% CI: 21.62–33.99%). Across the four seasons, the prevalence in spring, summer, autumn, and winter was 17.91% (36/201; 95% CI: 12.56–23.26%), 43.42% (208/479; 95% CI: 38.97–47.88%), 52.94% (27/51; 95% CI: 38.76–67.12%), and 47.44% (102/215; 95% CI: 40.71–54.17%), respectively. By breed, the prevalence was 40.21% (322/801; 95% CI: 36.80–43.60%) in commercial crossbred pigs and 35.17% (51/145; 95% CI: 27.21–43.04%) in Tibetan pigs. Three subtypes, ST1, ST3, and ST5, were identified, with ST5 being predominant (69.17%, 258/373), followed by ST3 (21.45%, 80/373) and ST1 (9.38%, 35/373). ST1 and ST5 were detected in all surveyed regions, whereas ST3 showed a more restricted geographic distribution. The detection of ST1, ST3, and ST5, which have also been reported in humans, suggests potential zoonotic relevance. However, the present findings do not establish direct transmission between pigs and humans. To our knowledge, this is the first detection of ST1 and ST5 in Tibetan pigs in China. Blastocystis was common in pigs in Yunnan Province. Its prevalence was significantly associated with geographic location, season, and age, and ST5 was the predominant circulating subtype. These findings reveal geographic and seasonal heterogeneity and regional subtype variation, supporting targeted surveillance and One Health investigations at the human–animal–environment interface.