Experimental infection of several fish species with the causative agent of Kuchijirosho (snout ulcer disease) derived from the tiger puffer Takifugu rubripes

Kuchijirosho (snout ulcer disease) is a fatal epidemic disease which affects the tiger puffer, Takifugu rubripes, a commercial fish species in Japan and Korea. To assess the possibility that non-tiger puffer fish can serve as reservoirs of infection, 5 fish species were challenged by infection with the extracts of Kuchijirosho-affected brains from cultured tiger puffer: grass puffer T. niphobles, fine-patterned puffer T. poecilonotus, panther puffer T. pardalis, red sea bream Pagrus major, and black rockfish Sebastes schlegeli, When slightly irritated, all these species, especially the puffer fish, exhibited typical signs of Kuchijirosho, i.e., erratic swimming, biting together and bellying out (swelling of belly), as generally observed in tiger puffers affected by Kuchijirosho, Although the mortalities of the 2 non-puffer species were lower, injection of the extracts prepared from the brains of both inoculated fish into tiger puffer resulted in death, indicating that the inoculated fish used in this experiment have the potential to be infected with the Kuchijirosho agent. Condensations of nuclei or chromatin in the large nerve cells, which is a major characteristic of Kuchijirosho, were histopathologically observed to some extent in the brains of all kinds of puffer fish species infected, These findings suggest that the virus can spread horizontally among wild and cultured puffers and even among fishes belonging to different orders.