Establishment of the complete life cycle of Calicophoron daubneyi under experimental conditions

The complex life cycle of the rumen fluke Calicophoron daubneyi is similar to that of the liver fluke Fasciola hepatica. Interestingly, C. daubneyi and F. hepatica share the same intermediate host, Galba truncatula. However, in contrast to its relative, experimental production of metacercariae is a major challenge for C. daubneyi, hampering a detailed analysis of its life cycle, especially in the definitive host. G. truncatula snails collected from natural habitats were bred in glass Petri dishes and fed dried organic lettuce leaves. C. daubneyi eggs were obtained from feces of naturally infected cattle and incubated until miracidia were hatching. Subsequently, these miracidia were allowed to infect snails, which were kept under specific laboratory conditions to monitor the shedding of metacercariae. In total, 177 G. truncatula snails were exposed to C. daubneyi miracidia during eleven snail infection trials. Sixty-eight of these snails survived for longer than 30 days post-infection (p.i.). From day 35 p.i., seven snails from five trials started shedding an average number of 106 metacercariae (range: 38-186) per snail. Three ewe lambs (aged 7-10 months) were inoculated orally with 150 metacercariae each. A different batch of metacercariae (obtained from three different snail trials) was used for each lamb. Another two lambs served as controls. All animals were regularly examined clinically, hematologically and coproscopically, using sedimentation techniques for the detection of trematode eggs. Low numbers of C. daubneyi eggs were detected in fecal samples of two of the three inoculated lambs on day 86 post-inoculation (yielding ≤ 2 epg), but only one lamb continued to shed eggs (up to 6 epg) until the end of the experiment (day 104 post-inoculation). None of the animals showed any abnormal clinical findings or blood parameters throughout the course of the study. Production of C. daubneyi metacercariae under laboratory conditions is reported, followed by experimental infection of the definitive host, thus completing the full life cycle of this parasite under experimental conditions. However, neither the survival rate of the snails nor the amount of metacercariae produced were comparable to previously published experiments using F. hepatica, necessitating further optimization of the laboratory protocols. Nevertheless, the results can serve as a starting point for more in-depth studies of this increasingly important trematode.