Hatchability of Fascioloides magna Eggs in Cervids

Abstract

The giant liver fluke (Fascioloides magna) is an invasive parasite found permanently in three foci in Europe. The fluke has an indirect life cycle involving a final and an intermediate host. The currently accepted terminology determines three types of final hosts: definitive, dead-end, and aberrant hosts. Recently, roe deer (Capreolus capreolus) has been classified as an aberrant host, which cannot contribute to the reproduction of F. magna. This study investigated the hatchability of F. magna eggs of red deer (Cervus elaphus) and roe deer origin to compare the suitability of the two host species for the maintenance of the parasite. The study was carried out on a newly invaded area, two years after the first reported observation of F. magna. The prevalence of the parasite proved to be 68.4% (CI95% 44.6–85.3%) in red deer and 36.7% (CI95% 24.8–50.0%) in roe deer. The difference between the two species was confirmed to be significant (p = 0.02). The mean intensity proved to be 10.0 (CI95% 4.9–22.6) and 7.59 (CI95% 2.7–24.2) in the red deer and the roe deer, respectively. The difference of the mean intensities did not prove to be significant (p = 0.72). Of the 70 observed pseudocysts, 67 originated from red deer and 3 from roe deer. Most of the pseudocysts contained two flukes, while a few pseudocysts contained one or three parasites. Egg production was observed in all three types of pseudocysts. We did not find more than three flukes in any pseudocyst. The apparent proportion of self-fertilisation in flukes without mating partners was 23.5% and 100% in red deer and roe deer, respectively. The survival of single-parent eggs was not confirmed to be worse than that of gregarious parents. The viability of offspring originating from roe and red deer differed significantly. Our findings suggest that F. magna adapted to the new populations of susceptible hosts rather than vice versa.

The Large American Liver Fluke (Fascioloides magna): A Survivor’s Journey through a Constantly Changing World

“…In Slovakia, the Vah/Vág and the Hron/Garam open gates to spread opposite the flow direction [73]. By the Croatian-Hungarian border river Drava, the same phenomenon can be observed [75,76,82,83].…”

“…In definitive hosts, the prepatent period is at least 30 weeks, and the lifespan of the flukes can reach five years [3]. In Europe, red deer (Cervus elaphus) and fallow deer (Dama dama) are confirmed to be definitive hosts [3,7], while the assessment of roe deer (Capreolus capreolus) has been varying recently [82,83].…”

“…arasitologia 2023, 3, FOR PEER REVIEW [3,7], while the assessment of roe deer (Capreolus capreolus) has been va [82,83]. In dead-end hosts, the parasite may reach sexual maturity similarly hosts.…”

“…In these cases, necropsy investigation of the carcasses did not detect pseudocyst formation [3,7,15] or egg production [72] in roe deer. Currently, increasing amounts of evidence confirm that in roe deer, pseudocyst development [91], egg production [82,83] and egg shedding [92] are common phenomena in endemic areas of Europe.…”

Identification and Molecular Characterization of Giant Liver Fluke (Fascioloides magna) Infection in European Fallow Deer (Dama dama) in Romania—First Report

“…Fascioloides magna has been reported in Croatia in C. capreolus [ 3 ], O. ammon musimon [ 19 ], S. scrofa [ 24 ], and C. elaphus [ 55 ]. It is speculated that the importation of F. magna into Europe induced not only host animal adaptations but also fluke adaptations to new intermediate and final hosts [ 3 , 46 ].…”