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. 2021 Feb 19:53:e2021-10.
doi: 10.21307/jofnem-2021-010. eCollection 2021.

First morphological and molecular identification of third-stage larvae of Anisakis typica (Nematoda: Anisakidae) from marine fishes in Vietnamese water

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First morphological and molecular identification of third-stage larvae of Anisakis typica (Nematoda: Anisakidae) from marine fishes in Vietnamese water

Hoang Van Hien et al. J Nematol. .

Abstract

Anisakid nematodes are parasites of cetaceans, their larval stages live in marine fishes. The third-stage larvae of some Anisakis species are also the etiological agents of human anisakiasis caused by consumption of raw or undercooked infected fish. Thus, identification of Anisakis larvae at the species level is crucial for their ecology and epidemiology. In Vietnam, although Anisakis larvae have been reported, they have not been identified to the species level. The aim of this study was, therefore, to identify third-stage larvae of Anisakis collected from marine fishes in Vietnamese water, based on morphological characteristics and molecular analysis. All Anisakis larvae found in this study were morphologically similar to each other and identical to Anisakis typica. In addition, molecular analysis based on ITS1-5.8S-ITS2 sequences confirmed them as A. typica. Vietnamese A. typica population was genetically close to those from Asian countries and Australia. The third-stage larvae of A. typica were collected from eight fish species from three localities in the South of Vietnam. Among them, seven were recorded as new intermediate hosts of A. typica. This is the first identification of A. typica larvae in Vietnamese water with records of new fish hosts.

Keywords: Anisakid larvae; Intermediate fish host; Molecular analyzes; Morphology; Vietnam.

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Figures

Figure 1:
Figure 1:
Study sites along the seashore of Vietnam. Three localities where fishes were infected with Anisakis larvae are print in bold.
Figure 2:
Figure 2:
Light micrographs of Anisakis typica larva. A. Whole larva; B. Anterior part of the body showing a long ventriculus; C. Anterior part of the body showing a boring tooth; D. Posterior end of the body showing a mucron.
Figure 3:
Figure 3:
Scanning electron micrographs of Anisakis typica larva. A. Anterior end showing a mouth and a boring tooth; B. Posterior end showing a mucron.
Figure 4:
Figure 4:
Phylogenetic tree reconstructed from ITS1-5.8S-ITS2 sequences of Anisakis typica from Vietnam and other Anisakis species. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. Bootstrap values are shown above the nodes. The nucleotide sequences obtained in this study are printed in bold, and others from the GenBank database are shown with Accession No., species name, and two letter country code of their geographical origin (AU: Australia, BR: Brazil, CN: China, DK: Denmark, GL: Greenland, IN: Indonesia, IE: Ireland, JP: Japan, MU: Mauritius, NO: Norway, PG: Papua New Guinea, PL: Poland, PT: Portugal, TH: Thailand, TR: Turkey, US: United States of America, VN: Vietnam).

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