TNP‐470, the analogue of fumagillin‐DCH, controls PKX in naturally infected sockeye salmon, Oncorhynchus nerka (Walbaum), underyearlings

Abstract

The use of fumagillin‐DCH, a natural product of Aspergillus fumigatus, has proven successful for the control of microsporidian infections, including Nucleospora salmonis Hedrick, Groff & Baxa (Hedrick, Groff & Baxa 1991) and Loma salmonae (Putz, Hoffmann & Dunbar) (Kent & Dawe 1994). Fumagillin has also been used to treat various myxosporean diseases of fishes, including proliferative kidney disease (PKD), which is caused by the PKX organism (Molnár, Baska & Székely 1987; Hedrick, Groff, Foley & McDowell 1988; Székely, Molnár & Baska 1988; Wishkovsky, Groff, Laurén, Toth & Hedrick 1990; Yokoyama, Ogawa & Wakabayashi 1990; El‐Matbouli & Hoffmann 1991; Sitjá‐Bobadilla & Alvarez‐Pellitero 1992; Higgins & Kent 1996). An analogue of fumagillin, TNP‐470, has been shown to be effective in in vitro studies against the mammalian microsporidian pathogens Encephalitozoon intestinalis (Cali, Kotler & Orenstein), Vittaforma corneae (Shadduck, Meccoli, Davis & Font) (Didier 1997), E. cuniculi Levaditi, Nicolau & Schoen and E. hellem Didier, Didier, Freidberg, Stenson, Orenstein, Yee, Tio, Davis, Vossbrinck, Millichamp & Shadduck (Coyle, Kent, Tanowitz, Wittner & Weiss 1998). Higgins, Kent, Moran, Weiss & Dawe (1998) tested TNP‐470 against two microsporidian diseases of salmonids, N. salmonis and L. salmonae, and showed a significant reduction in parasitism after oral treatment with 0.1 or 1.0 mg kg‐1 fish day‐1 for 5 weeks. Therefore, the present authors investigated the efficacy of TNP‐470 against the PKX myxosporean in naturally exposed sockeye salmon, Oncorhynchus nerka (Walbaum). This host was chosen as it has been found to be particularly susceptible to the infection.