| Summary: | In fish, as in other vertebrates, the alimentary canal is a primary route of infection with helminths. Of the 50 known species of Acanthocephalus, only 10 species have been recorded from Europe, of which 6 are from fish and 4 are from amphibians. With regard to the European records of Acanthocephalus from fish, eels, Anguilla anguilla (L.), collected from the Rhine River in Germany were found to harbour a new species, namely Acanthocephalus rhinensis. Later, this species was recorded in eels from Lake Piediluco, Central Italy. The topic of host specificity is interesting and has been given much attention. A total of 58 eels were collected from Lake Piediluco and 51 (87.9%) were infected with A. rhinensis, which was the most prevalent and abundant macroparasite found in the sample of eels. Some eels were co-infected with another acanthocephalan species, Dentitruncus truttae. From the stomachs of 2 eels, 109 intact and partially digested specimens of the amphipod Echinogammarus tibaldii were recovered and 16 (14.6%) of these were infected with 1-2 cystacanths of A. rhinensis per host. The whole DNA of 20 A. rhinensis (10 adult from A. Anguilla and 10 larvae from E. tibaldii) and 10 Dentitruncus truttae (5 from A. Anguilla and 5 from Salmo trutta) were extracted. The 18S rDNA PCR products (950 bp) were analysed by direct sequencing in the ABI 3730XL or ABI 3100 sequencing machines at BMR Genomics (Padua, Italy). Alignments were performed with Clustal W. The comparison of nucleotide sequence endorses whole heartedly the opinion that E. tibaldii is the intermediate host of A. rhinensis: the sequences obtained from the larvae and the adult are the same. This rDNA region is also useful to discriminate this specie from the other acanthocephalan species which co-occurred in A. anguilla from the lake Piediluco.
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