engleski

The ultrastructure of Anisakis spp. L3 larva

Genus Anisakis Dujardin, 1845 comprises nine species of marine parasitic nematodes, which utilize marine mammals as definitive hosts, and fish and cephalopods as paratenic hosts. Some of the members of this genus are the causative agent of the disease anisakiasis, contracted by consumption of raw or undercooked sea food contaminated with live third stage larvae (L3). Due to increasing trend of consuming raw or undercooked food, more cases of anisakiasis are reported each year, listing this zoonosis as an emerging public health concern. Despite their cosmopolitan distribution and high abundance, and extensive research being conducted, much remains unknown about their biology, especially their morphology at ultrastructural level. Our study presents the comprehensive ultrastructure of Anisakis spp. L3 larvae throughout the nematode body. Live L3 were cut into 1mm pieces representing different body regions and fixed by high pressure freezing/freeze substitution (HPF/FS). Fixed samples were then resin embedded, cut to ultrathin sections, double contrasted and inspected under 80 kV microscope. Muscle layer, located below multi-layered cuticle, is composed of elongated cells with large pale areas in non-contractile part indicative of glycogen storage. Epithelial cells of alimentary tract, except for oesophagus, are lined with microvilli and contain many different vesicles and multivesicular bodies. Single-celled excretory gland is composed of tightly packed vesicles of different size, surrounding large nucleus, which open into one main and several minor collecting ducts. All nuclei appeared rich in euchromatin with a single nucleolus, except for excretory gland nucleus that contains many nucleoli. In the hind part of the worm, several exosomal vesicles were found, containing same amorphous matter lining the cuticle from the outside. Presence of countless different vesicles and their localisation in intestinal cells and excretory gland, rich rough endoplasmic reticulum and euchromatin suggests active synthesis of secreted products, which aid the infective larvae in invading host tissue.

Anisakis ; ultrastructure ; transmission electron microscopy

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