Prevalence of anisakid parasites in fish collected from Apulia region (Italy) and quantification of nematode larvae in flesh

Anisakis spp. and Hysterothylacium spp. are nematodes that commonly parasitize several fish species. Nematode larvae can be recovered in coelomic cavity and viscera, but also in flesh and have an important economic and public health impact. A total of 1144 subjects of wild teleosts, 340 samples of cephalopods and 128 specimens of farmed fish collected from Apulia region were analysed for anisakid larvae detection by visual inspection of coelomic cavity and viscera and by digestion of the flesh. No nematode larvae were found in farmed fish and cephalopod molluscs. All examined wild-caught fish species were parasitized, except for 5 species for each of which only a few subjects belonging to the same batch were sampled, therefore the results are just indicative. A total of 6153 larvae were isolated; among these, 271 larvae were found in the muscular portion. Larvae were identified by morphological method as belonging to the genera Anisakis (97.2%) (type I and type II) and Hysterothylacium (2.8%). Both nematodes could be found in all fish species, except for round sardinella (Sardinella aurita), infected only by Hysterothylacium spp. and for Mediterranean scaldfish (Arnoglossus laterna), little tunny (Euthynnus alleteratus) and chub mackerel (Scomber japonicus) infected only with Anisakis spp. A sample of 185 larvae was sent to the National Reference Centre for Anisakiasis (C.Re.N.A.) of Sicily for identification at the species level: 180 larvae belonged to the species A. pegreffii and 2 larvae to A. physeteris. The remaining 3 larvae were identified at genus level as Hysterothylacium. Statistical indices such as prevalence, mean intensity and mean abundance were calculated. Chub mackerel (S. japonicus) was the species with the highest prevalence and mean intensity. Moreover, the average and the median values of larvae per 100 g of edible part for each fish species were determined to estimate the consumer exposure to Anisakis spp. The obtained values were then recalculated by referring to the edible part of all specimens (infected and non-infected) forming a single parasitized batch, getting more realistic and objective data useful for risk assessment. Our results indicate that the consumption of raw or undercooked wild fish caught off Apulian coasts could result in the acquisition of anisakiasis; on the contrary, farmed fish and cephalopods appear to be safer for the consumer.