Effect of Cestodes Parasitizing the Small Intestine on Host Protease Activities in Herring Gull Chicks.

Total protease activity and activities of protease subclasses in the small intestine were assayed in herring gull (Larus argentatus (Pontoppidan, 1763)) chicks infested by the cestodes Tetrabothrius erostris (Loennberg, 1889) (Cestoda: Tetrabothriidae), Microsomacanthus ductilus (Linton, 1927) (Cestoda: Hymenolepididae), Wardium cirrosa (Krabbe, 1869) (Cestoda: Aploparaksidae), Arctotaenia tetrabothrioides (Loennberg, 1890), and Alcataenia larina (Krabbe, 1869) (Cestoda: Dilepididae). Serine protease activity was found to decrease in small intestine sites with the highest cestode abundance (M. ductilus in the proximal segment; W. cirrosa in the distal segment; and Ar. tetrabothrioides, T. erostris, and Al. larina in the medial segment). Cysteine protease activity increased in sites of M. ductilus, W. cirrosa, and Al. larina location. Protease absorption on the tegument surface was observed in all of the cestodes under study, and serine proteases accounted for a major part of the absorbed enzymes. Homogenates of W. cirrosa, M. ductilus, Ar. tetrabothrioides, T. erostris, and Al. larina were shown to inhibit activities of host proteases and commercial trypsin.