イルカ集団自殺の原因としての寄生虫性内耳神経炎

抄録

In the early morning on Jan. 6, 1982, 135 cetaceans were found stranded alive at Aoshima Beach, Miyazaki, Japan. Since Aristotle reported on the strnading of dolphins, single or mass stranding of various kinds of cetaceans have been reported from many parts of the world. However, the reason for such mass stranding is not still fully explained to everyone's satisfaction.
We have examined one of them and found a lot of parasites in the bilateral tympanic cavities. The parasites were identified to belong to the genus Nasitrema and closest to Nasitrema gondo Yamaguchi. The number of the parasites were over 30 in each ears, and the mucous membrane of the cavity was inflammed. The ossicular chain was fixed especially the stapes was fixed at the oval window. The periotic bone including the labyrinth was studied histologically. In the labyrinth pathological changes were minimum. However, the octavus nerve was inflammed and many eggs with triangular shape in cross section were found near the nerve. From the findings obtained, we would like to conclude that parasitogenic otitic and octavus neuropathy should be a possible cause of live mass stranding of cetaceans.