Mutation scanning-based analysis of anisakid larvae from Sillago flindersi from Bass Strait, Australia

Anisakidosis is an important fish-borne disease caused by the larvae of anisakid nematodes, which affects humans and a range of other animals. The accurate identification of members of this nematode group is central to investigating the epidemiology of the parasites and in the surveillance and control of anisakidosis. It is now well known that morphological identification alone does not allow specific identification, particularly of larval stages. To better understand the epidemiology of anisakid nematodes in southern Australian fishes and the potential risks posed to human health, a survey of 50 specimens of the commercially important fish, Sillago flindersi, from Bass Strait, Australia was conducted. We characterised anisakid larvae by PCR-coupled mutation scanning, sequencing and phylogenetic analyses of the first and second internal transcribed spacers (ITS-1 and ITS-2) of nuclear ribosomal DNA. This study revealed that 92% of the S. flindersi examined were infected with anisakids (n=194), which were represented by seven genotypes. Phylogenetic analyses of the genotypes defined herein, together with reference sequence for Anisakis pegreffii and Hysterothylacium sp. from public databases (i.e. GenBank), revealed the presence of A. pegreffii (n=24), Hysterothylacium larval type IV (n=90) and Hysterothylacium larval type VIII (n=80) in S. flindersi. Thus, the PCR-coupled mutation scanning approach employed herein is an effective tool for the genetic characterisation of anisakid nematodes for diagnostic and analytical purposes (nucleotide sequences reported in this paper are available in the GenBank database under accession nos. JN631796-809).