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Information on longevity of digeneans is restricted to a few studies on some medically important species (see review in Sandground, 1936). Thus, fasciolids may persist in various ruminants for 5 years or more and human schistosomes and opisthorchids may live for 20-30 years. However, most digeneans survive in their definitive hosts for several months or 1-2 years (Sandground, 1936). Precise information on the longevity of adult non-human digeneans in laboratory hosts is, for the most part, unavailable. In most studies on digeneans in laboratory hosts, the experiments were terminated prior to the time when all adult worms were eliminated from the hosts (see, for example, Toledo et al., 2005).
Hosier & Fried (1991) determined the longevity of the intestinal trematode Echinostoma caproni in ICR mice; the study was not terminated until 29 weeks postinfection (PI) and showed that mice, each infected with 25 encysted metacercariae (cysts), could support a relatively high percentage of worms up to 20 weeks PI. From 20 to 29 weeks PI, there was a diminution in worm growth (degrowth) based on body area measurements. There was also an anteriad shift in the worm population from the ileum-jejunum to the duodenum. The duodenum is an unusual site for this digenean (see review in Fried &...