Occurrence and viability of Anisakis spp. larvae in ready to eat products made of herring (Clupea harengus) sold in Italy

The study aimed to assess the occurrence and viability of Anisakis spp. larvae in ready to eat products made of herring, a common host of Anisakis spp. and the third most commercialized fish species in the EU. A total of 135 products consisting of 50 smoked whole specimens and 85 filleted products (25 smoked, 30 marinated, 30 canned) were sampled from 2016 to 2018. Viscera and muscle of whole herrings were visually inspected and separately digested. Filleted products were also visually inspected and digested. Larvae viability was assessed, then they were counted and microscopically identified to genus level. A subsample was molecularly identified. At least one Anisakis spp. larva was found in 56 products (41.5%), for a total of 1715 larvae collected (0-172 larvae/product). Most of the larvae (91%) were found in the viscera of 49 of the 50 whole herrings (98%). A highly significant difference was observed between the positivity rate and larval density at muscle level, as 149 larvae were found in the muscle of 31 whole herrings (positivity rate 62%, 0.022 larval density/g), while only 7 larvae were found in the 85 filleted products (positivity rate 7%, 0.001 larval density/g). Larvae were molecularly identified as A. simplex. The study showed that obviously contaminated products are commercialized. All the larvae were dead, proving a negligible risk of developing anisakiasis. However, their allergenic potential is debated and the significant difference between muscle infection levels in whole and filleted herrings may result in a different risk of exposure to antigens.