A myxozoan parasite Kudoa septempunctata causing the food poisoning of humans which consume raw olive flounder Paralichthys olivaceus has become a new threat to public health. This review focuses the recent occurrence of K. septempunctata-induced food poisoning in Japan for 10 years, the typical symptoms of the foodborne disease in humans, parasitology, diagnoses, countermeasures and the remaining issues. The numbers of K. septempunctata-induced cases and patients have peaked in 2014, followed by a gradual decrease in recent years. The symptoms of humans are characterized by transient vomiting and diarrhea. Also, onset of the disease is dose-dependent of fresh spores (> 1 × 107). The host fish for K. septempunctata is mainly limited to P. olivaceus. The geographical distribution is Japan and Korea. The two locality isolates are easily differentiated by a ratio of spores possessing 7 polar capsules. The light-microscopy, conventional or real-time PCRs, LAMP, immunochromatography have been developed for the diagnostic tools. To prevent the infection with K. septempunctata in juvenile stage of cultured flounder, a sand-filtration combined with ultraviolet irradiation (> 46 mJ/cm2) is effective. At the time of shipment of adult flounder, light-microscopic examination for spores is recommended to remove the infected fish group. The remaining problems include the disease mechanisms in humans, the host range, and the harmful Kudoa species other than K. septempunctata.
