The giant liver fluke in Europe: A review of Fascioloides magna within cervids and livestock with considerations on an expanding snail-fluke transmission risk

The giant liver fluke, Fascioloides magna, common in North America and introduced into Europe in the 19th century, is an underappreciated model system for epidemiological studies on biological invasions, interactions with other native parasites and for health impact assessments within both definitive and intermediate snail host populations. Owing to its first contemporary appearance in Europe and then its subsequent spread, fascioloidosis has become a fluke-livestock/wildlife-snail combination of increasing interest for veterinarians, parasitologists and population geneticists. Here, we present a description of its recent epidemiology, biogeography and biology, inclusive of host species lists. Special emphasis is placed upon known definitive hosts of F. magna within Europe and considerations upon this fluke's local intermediate snail hosts. This helps us envisage plausible future epidemiological scenarios for further expansion across Europe, potentially even invasion into the UK. In line with others who draw attention upon needs for better systematic monitoring of putative risk-areas of fluke transmission, we close by highlighting why better surveillance of F. magna across continental Europe, and neighbouring territories, is justified.

Wild Boar (Sus scrofa)—Fascioloides magna Interaction from the Perspective of the MHC Genes

Fascioloidosis is a parasitic disease caused by a trematode Fascioloides magna. Since major histocompatibility complex (MHC) genes play an important role in the immune response, the aim of this study was to compare the potential differences in MHC class II SLA-DRB1 exon 2 genes between wild boar populations from infected (cases) and non-infected areas (controls). During the winter of 2021, a total of 136 wild boar tissue samples were collected, 39 cases and 97 controls. DNA was extracted and sequenced using the Illumina platform. Differences in distributions of allele combinations were calculated using the Chi-Square test for homogeneity and between proportions using the large-sample test and Fisher–Irwin test. Analysis revealed 19 previously described swine leucocyte antigen (SLA) alleles. The number of polymorphic sites was 79 (29.6%), with 99 mutations in total. Nucleotide diversity π was estimated at 0.11. Proportions of the alleles SLA-DRB1*12:05 (p = 0.0008379) and SLA-DRB1*0101 (p = 0.0002825) were statistically significantly higher in controls, and proportions of the SLA-DRB1*0602 (p = 0.006059) and SLA-DRB1*0901 (p = 0.0006601) in cases. Alleles SLA-DRB1*04:09, SLA-DRB1*0501, SLA-DRB1*11:09, and SLA-DRB1*1301 were detected only in cases, while SLA-DRB1*0404, SLA-DRB1*0701, SLA-DRB1*02:10, and SLA-DRB1*04:08 were present only in controls. We did not confirm the existence of specific alleles that could be linked to F. magna infection. Detected high variability of the MHC class II SLA-DRB1 exon 2 genes indicate high resistance potential against various pathogens.

Sika Deer (Cervus Nippon) are not "Dead-End Hosts" of the Giant Liver Fluke, Fascioloides Magna (Bassi, 1875) Ward, 1917

Fascioloides magna, although of North American origin, is well established in central Europe. Here it is expanding its geographic range and has been exposed to new potential final hosts including native and naturalized species. Based on their contribution to the propagation and transmission of F. magna, its final hosts were grouped by Pybus into three types, including 'dead-end hosts' that comprise species in which flukes reach the liver but rarely mature and produce few eggs which are not excreted. Sika deer (Cervus nippon) were classified as dead-end hosts, this being quoted in the literature without robust substantiation. In an investigation on the occurrence of F. magna among sympatric wild ungulates in a recently established focus of the parasite in Germany, nine of 24 sika deer were found infected with up to seven F. magna in their livers, and six of the fluke-positive sika deer had Fascioloides eggs in their feces. Most flukes were recovered in pairs from fibrous capsules. Associated with the low fluke burden, gross pathology of the livers was generally mild. The presence of mature flukes in fibrous capsules, and passing of ova in the feces, demonstrates sika deer to be suitable definitive hosts of F. magna and to be of epidemiologic significance because of their implication in the transmission of the fluke.

Complementary liver and serum protein profile in wild boars infected by the giant liver fluke Fascioloides magna using tandem mass tags quantitative approach

Liver fluke, Fascioloides magna, is an important non-native parasite introduced to Europe, posing a threat to survival of local wildlife populations. The aim of this study was to assess the serum and liver protein profile of control and F. magna infected wild boars, by means of shotgun tandem mass tag - based quantitative high resolution proteomics approach. In serum, 4 differentially abundant proteins were found out of total 1073 identified, while in liver from 3520 identified proteins, 116 were differentially abundant between healthy and F. magna infected wild boars. Pathway analysis revealed that most of the proteins differing in abundance are involved in metabolism, biological oxidations, cellular responses to stimuli, fatty acid metabolism, and others. Validation of proteomic results was performed for paraoxonase-1, ceruloplasmin, glutathione S-transferase and liver enzymes by ELISA and automated assays. Complementary analysis of liver and serum in F. magna infection enabled insight into changes of proteome profile of the host at local and sistemic level. Our findings showed that chronic infection with F. magna is associated with immune response in host, oxidative stress and metabolomic changes in liver. SIGNIFICANCE: Liver fluke infections are recognised as worldwide neglected diseases with considerable veterinary and public health importance. Pathological changes, clinical signs and outcome of F. magna infection are strongly related to the type of final hosts and their different tolerance to infection. In order to gain insight into host-parasite interactions in wild boars, dead-end host for F. magna, we assessed proteomics profile of serum and liver of control animals and those infected with F. magna. Proteomics analysis of serum and liver in parallel showed as advantageous and beneficial, demonstrating protein alterations mainly at local level. Bioinformatics analysis enabled elucidation of molecular pathways associated with F. magna infection. Identification and validation of proteins associated with infection may have added value to current tools for efficient liver fluke control.

First record of chronic Fascioloides magna infection in roe deer (Capreolus capreolus)

Fascioloidosis is an allochthonous parasitic disease in Europe caused by the digenean trematode Fascioloides magna. The final hosts of F. magna in Europe are defined as definitive, aberrant and dead-end. Roe deer are aberrant hosts in which juvenile flukes permanently migrate through the liver parenchyma. Failure in pseudocysts formation leads to the death of both the host and the parasite. In this paper we present gross and histological findings of F. magna infection in 34 roe deer. The special emphasis is on the pseudocyst formation accompanied with new fluke's migratory channels observed in 7 animals, suggesting reinfection and prolonged survival of roe deer. No F. magna eggs were recovered from the faeces of the infected animals. These findings indicate that pseudocyst formation is essential for roe deer survival, but also point out the potential beginning of adaptation processes in roe deer, altering otherwise acute and fatal disease into a chronic one.

The Prevalence and Degree of Endoparasitic Infections in Wild Boars Using the Semi-quantitative Fecal Egg Count Method

PURPOSE

Breeding of wild boars is a significant part of the hunting economy; however, hogs are associated with zoonotic infection. This study assessed the prevalence and degree of parasitic infections that exist in wild boars from two hunting grounds in the Autonomous Province of Vojvodina, Republic of Serbia.

METHODS

Parasitological examinations were conducted from 2016 to 2019. In total 220 fecal samples and 13 lungs were collected from wild boars in two hunting grounds (an open and a closed habitat) on the territory of Vojvodina (Serbia). Assessment of the prevalence and degree of the detected endoparasitosis involved a semi-quantitative fecal egg count method.

RESULTS

The presence of protozoa-Eimeria spp./Isospora spp. (76.38%; 32.26%) and Balantidium coli (7.08%), nematodes-Ascaris suum (29.03%), Trichuris suis (31.49%; 19.35%), Hyostrongylus rubidus/Oesophagostomum spp. (55.12%; 48.39%), Metastrongylus pudendotectus (66.14%; 21.51%), Gnathostoma hispidum (3.94%; 2.15%) and Macracanthorhynchus hirudinaceus (9.45%; 7.53%) and trematodes-Fasciola hepatica (5.51%; 4.30%) and Dicrocoelium dendriticum (0.78%; 2.30%) were detected as single or mixed infections, via qualitative coprological examination. The total prevalence of the endoparasitosis was 92.91% in hunting ground I (closed habitat) and 73.12% in hunting ground II (open habitat). The most prevalent infection in hunting ground I was coccidiosis (76.38%), and hyostrongylosis/oesophagostomosis (48.39%) in hunting ground II. Adult forms of M. pudendotectus were identified in the lungs of 13 wild hogs with mild to severe bronchopneumonia from hunting ground II.

CONCLUSIONS

The semi-quantitative fecal egg count method demonstrated clinical and parasitological significance and revealed the risks associated with zoonotic infections in this game species population. Therefore, monitoring the etiology and epizootiology of parasitic infections in wild boars is essential for creating health care programs in hunting ground areas and planning control strategies that protect both the hunting economy and public health.

Occurrence of the giant liver fluke, Fascioloides magna, in sympatric wild ungulates in one area in the Upper Palatinate Forest (northeastern Bavaria, Germany)

Associated with the spreading in (north)western direction of Fascioloides magna from its historic endemic area in Bohemia with its cervid hosts, unusual noticeable hepatic lesions (black-colored tissue, hemorrhage) were observed in deer harvested in hunting grounds and one deer farm located in the Upper Palatinate Forest close to the border to the Czech Republic, initially in the years of 2007 and 2009, respectively. Confirmation of the suspected diagnosis of F. magna infection in October 2011 prompted investigations on the occurrence of "fascioloidosis" among wild ungulates in that locality. From October 2011 to January 2014, livers from 89 cervids and two wild boars were examined for flukes. Thirty-seven livers (40.6%) harbored F. magna: 17 of 21 red deer, nine of 24 sika deer, six of eight fallow deer, four of 36 roe deer, one of two wild boars. Fluke burdens ranged from 2 up to 151 in red deer, from 2 up to 37 in fallow deer, and from 1 up to 7 in sika deer and in roe deer; one fluke was recovered from the liver of one wild boar. No other parasites were recovered from the livers. The rate of recovery of F. magna differed significantly (p < 0.001) among the species of deer (red deer, 81.0%; sika deer, 37.5%; fallow deer, 75.0%; roe deer, 11.1%) and between the age groups (< 1 year: 22.2%, 1 to 2 years: 26.0%, and > 2 years: 70.0%, respectively). There was no association (p > 0.1) between the rate of recovery of F. magna and the sex of the combined 80 deer of ≥ 1 year of age (male: 41.8% and female: 31.4%). The occurrence of F. magna in the wild ungulates in the Upper Palatinate Forest area in northeastern Bavaria is of epidemiological importance for the further spreading of the parasite into Germany with migrating deer.