Molecular epidemiology of Blastocystis in pigs and their in-contact humans in Southeast Queensland, Australia, and Cambodia

Blastocystis, an intestinal protist commonly found in humans and animals worldwide, has been implicated by some as a causative agent in irritable bowel syndrome in humans. In pigs, infection with Blastocystis is commonly reported, with most pigs shown to harbour subtypes (ST) 1 or 5, suggesting that these animals are potentially natural hosts for Blastocystis. Although ST5 is considered rare in humans, it has been reported to be a potential zoonosis from pigs in rural China. To test these hypotheses, we conducted molecular analysis of faecal samples from pigs and in-contact humans from commercial intensive piggeries in Southeast Queensland (SEQ), Australia, and a village in rural Cambodia. The prevalence of Blastocystis in SEQ and Cambodian pigs was 76.7% and 45.2%, respectively, with all positive pigs harbouring ST5. It appears likely that pigs are natural hosts of Blastocystis with a high prevalence of ST5 that is presumably the pig-adapted ST in these regions. Amongst the SEQ piggery staff, 83.3% were Blastocystis carriers in contrast to only 55.2% of Cambodian villagers. The predominant STs found in humans were STs 1, 2 (Cambodia only) and 3. Interestingly, ST5 which is usually rare in humans was present in the SEQ piggery staff but not in the Cambodian villagers. We conclude that in intensive piggeries, close contact between pigs and their handlers may increase the risks of zoonotic transmission of Blastocystis.