Two cases of cutaneous gnathostomiasis after eating raw Salangichthys microdon (icefish, shirauo)

Cutaneous gnathostomiasis (CG) is a disease caused by ingestion of third-stage Gnathostoma larva in raw snakes, freshwater fish or frogs. The common causative organisms of CG in Japan include G. nipponicum, G. spinigerum, G. doloresi, G. binucleatum and G. hispidum. We report two cases of CG after eating many raw Japanese icefishes (Salangichthys microdon). In both cases, linear itchy eruptions on the trunk developed after eating many S. microdon. We performed genetic analysis in the first case, which revealed G. nipponicum. Of note, this is the first case of CG diagnosed based on genetic analysis in Japan. In Japan, eating whole small raw freshwater fish is common. The most popular types of raw small freshwater fish consumed in Japan are S. microdon (shirauo in Japanese) and Leucopsarion petersii (shirouo in Japanese). Usually, S. microdon are born in rivers, but live in both the sea and rivers. They feed on small fish and freshwater water fleas and spawn in rivers in the spring. On the other hand, L. petersii are born in rivers, but move to the sea soon after hatching. They feed on plankton such as copepod in the sea. They do not feed on anything when they return to rivers to spawn in the spring. Therefore, we hypothesize that S. microdon are more easily parasitized by G. nipponicum.