Current Status of Anisakiasis and Larvae in Tokyo, Japan.

Anisakiasis is a gastrointestinal disease caused by infection with anisakid nematodes. larvae have been listed as distinct food poisoning agents in the manual of Food Poisoning Statistics, Japan since 2013. The reported numbers of food poisoning cases caused by larvae are gradually increasing. A total of 94.0% of the causative larvae species were identified as sensu stricto (), and 4.4% were identified as , among human-isolated anisakid nematodes examined in Tokyo Metropolitan Institute of Public Health, Japan from 2011 to 2018. species infecting fishes in Japanese waters differ depending on their habitat and depth. mainly infects fishes in the Pacific side of Japan, and mainly infects fishes in the East China Sea and Sea of Japan sides. Regarding the causative foods of anisakiasis, cases by ingestion of mackerel ( spp.) have been the most common in Japan, and cases caused by eating "marinated mackerel" accounted for 32.8% of the total in Tokyo from 2011 to 2017. However, the number of reports of food poisoning caused by skipjack tuna () was highest in May 2018 in Japan. A parasitological surveys of third-stage larvae in skipjack tuna in Japanese waters were conducted in 2018 and 2019, and it was confirmed that more infections of skipjack tuna may have occurred in 2018 than usual due to the meandering flow of the Black Current. Moreover, a portion of larvae migrated from visceral organs to the ventral muscle in live skipjack tuna before capture, suggesting that an extensive cold chain after capture cannot prevent anisakiasis. In fish species that were reported to be high frequency of causative food of anisakiasis, it is necessary to freeze or at least remove the ventral muscle.