Phylogenetic and phylogeographic analyses of Anisakis simplex sensu stricto (Nematoda: Anisakidae) from the common minke whale in Korean waters

Abstract

The genus Anisakis is among the most significant parasites to public health, as it causes anisakiasis, a parasitic infection in humans resulting from consuming raw or undercooked seafood. Although the infection status of i>Anisakis in second intermediate hosts, such as marine fishes and cephalopods, and humans have been severally reported in Korea, no information about the definitive host in Korean waters is available. In 2014, 2 adult gastric nematodes were collected from a common minke whale (Balaenoptera acutorostrata) found in the East Sea, Korea. These worms were identified as A. simplex sensu stricto (s.s.) by comparing the mitochondrial COX2 marker with previously deposited sequences. Phylogenetic and phylogeographic analyses of A. simplex (s.s.) worldwide revealed 2 distinct populations: the Pacific population and the European waters population. This is the first report on adult i>Anisakis and its definitive host species in Korea. Further studies on Anisakis infection in other cetacean species and marine mammals in Korean seas are warrantedi>Anisakis.

Keywords: Anisakis sp.; COX2; common minke whale; nematoda; phylogenetic analysis.

Fig. 1

Adult worms and an egg of Anisakis simplex sensu stricto (s.s.) recovered from the common minke whale, Balaenoptera acutorostrata. (A) Two female adult Anisakis simplex (s.s.). (B) The egg of Anisakis simplex (s.s.) observed under a light microscope.

Fig. 2

A concatenated phylogenetic tree from Bayesian inference (BI) and max likelihood (ML) analyses of the mitochondrial cytochrome oxidase 2 (COX2) datasets constructed based on the GTR+I+G model of evolution. The newly generated sequence in this study is indicated in bold. Posterior probability values (≥0.80) and bootstrap values (≥85) are given on the branches. The branch length scale bars indicate the number of substitutions per site. According to the BI and ML phylogenetic analyses using the COX2 marker, the Anisakis simplex (s.s.) sequences formed 2 highly supported clades.

Fig. 3

Genealogical relationships among 69 mitochondrial COX2 marker haplotypes of Anisakis simplex (s.s.) from 5 different sea areas inferred from all available GenBank sequences based on a median-joining (MJ) network. The diameter of each circle is proportional to the number of specimens. The short vertical lines indicate single mutational differences between the 2 haplotypes connected. Circle colors represent geographical origins from which particular anisakid haplotypes were sampled.