Molecular detection of myxosporean parasites in human fecal samples associated with foodborne illness

In 2011, Kudoa septempunctata (Myxozoa: Myxosporea: Multivalvulida) was recognized as a causative agent of foodborne illness in Japan. Since then, studies have conducted surveillance for this parasite in flounder, a primary vehicle for foodborne outbreaks, and have reported the detection of K. septempunctata in fecal samples from patients. Although sporadic outbreaks suspected to be associated with the consumption of fish other than flounder have also been reported, information on examination of patient feces or leftover fish in such outbreaks remains limited. In this study, we investigated the detection of Kudoa and Unicapsula genes in patient fecal samples and the presence of myxosporean parasites in fish associated with diarrheal incidents following the consumption of raw fish. Kudoa and Unicapsula genes were detected in 29.2% of 144 fecal samples analyzed, with the highest detection rate in Kudoa hexapunctata-positive incidents. The fecal detection rate was significantly higher when samples were collected within four days after fish consumption, particularly in incidents involving K. hexapunctata and Unicapsula seriolae, while detection rate declined in samples collected after five days. Myxosporean parasites were identified in 84.6% of leftover fish samples, whereas fish from another batch prepared at the same facilities consistently tested negative. The higher fecal detection rate observed in K. hexapunctata incidents may reflect higher spore ingestion from tuna, the host for this parasite, due to larger portions. These findings emphasize the importance of timely investigations and testing of fecal samples within four days of consumption and leftover fish samples in suspected myxosporean diarrhea outbreaks.