Fasciola hepatica miracidia are dependent on respiration and endogenous glycogen degradation for their energy generation

It is generally accepted that free-living stages of parasitic helminths are dependent on aerobic degradation of endogenous energy sources for their en ergy generation. This concept, however, is not the result of extensive expe rimental evidence, but originated mainly intuitively as oxygen is widely av ailable in their habitat and these stages generally have a small size. Schi stosoma mansoni, the sole parasitic helminth whose energy metabolism has be en studied throughout its life-cycle indeed has aerobically functioning fre e-living stages. However, large differences exist in energy metabolism betw een adult stages of distinct parasitic helminths, and caution should be tak en in predicting that all free-living stages of all parasitic helminths hal e the same, aerobic energy metabolism. Hence, this report studied the energ y metabolism of Fasciola hepatica miracidia and demonstrated that F. hepati ca miracidia are also dependent on aerobic degradation of their endogenous glycogen stores by glycolysis and on Krebs cycle activity for energy genera tion. However, in contrast to S. mansoni, F. hepatica miracidia cannot func tion anaerobically, as inhibition of the respiratory chain blocked motility and carbohydrate degradation, and finally resulted in death of the miracid ia. Therefore, this report demonstrated that differences exist between mira cidia of distinct species, in pre-adaptation of their energy metabolism to the occasional hypoxic conditions within their next host.