Digenean trematodes in Hungarian freshwater aquacultures

Abstract

Occurrence of metacercariae of potentially zoonotic trematodes (Platyhelminthes: Digenea) in the musculature of common carp ( Cyprinus carpio L. 1758) was monitored in four Hungarian aquacultures. Four geographically distinct fish farms (located in the Northwestern, Southwestern, Northeastern and Southeastern parts of Hungary) were selected for the investigation. From each farm, a total of 258 one-summer-old fingerlings were sampled and examined in the years 2016 and 2017. In addition, in 2017, we examined 60 market size specimens (30 two-summers and 30 three-summers) sampled from the most infected aquaculture in the Northeastern part of Hungary. The fish were euthanized and decapitated whereafter their musculature (fillets) was digested in a pepsin solution to isolate metacercariae from the tissue whereafter morphological and molecular analyses (PCR and sequencing of ITS region) were performed. Opisthorchiid metacercariae were not recovered but in one of the farms numerous metacercariae were detected in the musculature of carp. They were identified as cyathocotylid trematodes based on their morphological characteristics and by sequencing the ITS region. The infection levels proved to be remarkably different among the four fish farms. Carps from the Northeastern farm were infected by large numbers of cyathocotylid metacercariae, while 8 Posthodiplostomum cuticola metacercariae were detected in the Northwestern aquaculture. In the other two farms (Southwestern and Southeastern) no infection was recorded. The infected farm is located close to a protected natural wetland habitat populated by a rich fauna of aquatic birds (potential final hosts) and snails (first intermediate host) which may create a higher risk of infection in the neighbouring fish farms.

The Occurrence of Freshwater Fish-Borne Zoonotic Helminths in Italy and Neighbouring Countries: A Systematic Review

“…The occurrence of FBZHs was registered only in wild fish species. This is in agreement with the literature data on other freshwater [25] and marine [26][27][28] species, stating that the risk related to the consumption of aquaculture products from European facilities is null or negligible. The absence of zoonotic parasites in aquaculture products, which was more extensively investigated for marine FBZHs, is mainly related to the use of commercial pellets as feed, which avoids the predation of infected intermediate hosts by farmed fish [29,30].…”

Phylogeny and morphology of some European cyathocotylid digeneans (Trematoda: Diplostomoidea)

“…Adult specimens of P. ovatus examined in our study clustered in one strongly supported clade with the metacercariae from Hungarian and Italian fishes originally classified by Cech et al . (2021) as Cyathocotylidae gen. sp. (available in GenBank NCBI as Holostephanus sp.).…”

Re‐evaluation of certain aspects of the EFSA Scientific Opinion of April 2010 on risk assessment of parasites in fishery products, based on new scientific data. Part 1: ToRs1–3

“…It could therefore be expected that cultured carp is exposed to infection. However, a parasitological survey of cultured common carp in Hungary did not detect these parasites, and the metacercariae found were non‐zoonotic (Cech et al., 2021 ; Sándor et al., 2020 ). Monitoring data from other major carp producing countries including Poland, Czechia and Germany are lacking.…”