Cestodes (tape worms)
Cestodes are tapeworms with segmented bodies and a structure that allows them to attach to the intestinal wall of their hosts. Diphyllobothrium latum a broad tapeworm is the species of most concern. D. latum parasites are distributed worldwide. A similar species is found in the southern latitudes and is associated with seal hosts. Cases have been reported worldwide, including Australia. It is the largest human tapeworm, growing up to 10 metres (FDA 2003).
Fish are intermediate hosts and infective larvae have been found in trout, whitefish, pike and salmon. Cestode larvae found in fish range from a few millimetres to several centimetres in length and are white or grey in colour. Diphyllobothrium tapeworms primarily infect freshwater fish, but salmon and related fish can also carry the parasite. Diphyllobothrium tapeworms are usually found unencysted and coiled in musculature or encysted in viscera (M&S Food Consultants 2001).
Diphyllobothrium spp. have been reported to be present in Australian fish (Humphrey 1995) but there is little detail of the parasite species or species of fish affected.
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