2016 Volume 21 Issue 4 Pages 141-144
Over the past five years since 2010, waterfowl individuals with protruded eyeballs were observed within an overwintering population at Saigawa River in Azumino City, Nagano Prefecture, Japan. From the protruded eyeballs in an individual of the tundra swan Cygnus columbianus, a leech specimen in the genus Theromyzon. （Annelida, Hirudinea）was collected； the digestive tract of the leech contained blood including avian erythrocytes. Due to the poor condition of the specimen, however, it was not identified down to the species level, although other specimens from the waterfowls’ roost pond were positively confirmed to be T. tessulatum. The waterfowl eyeball protrution can be mainly caused by T. tessulatum parasitism.
