The NE Atlantic European hake: A neglected high exposure risk for zoonotic parasites in European fish markets

A sampling programme to understand the factors affecting zoonotic parasite presence and infection intensity of Atlantic European hake populations was conducted from 2013 to 2015. Commercial fish samples comprising 430 hake specimens from northern (Grand Sole) and southern (Atlantic Iberian Peninsula) fishing grounds were sampled, recorded and inspected. We also analysed 75 additional samples collected around Scotland. Parasites were microscopically identified to genus level. Fish biometric measurements were statistically evaluated as categorical predictors of parasite recruitment into fish stocks. Stable isotope composition was determined in another sample batch of 501 hakes from the NE Atlantic (Grand Sole and Galician grounds) to explore trophic indicators as potential predictors of parasite burden. Partial sequences from mitochondrial and nuclear marker genes (mtDNA cox2 and EF1 α-1 nDNA) from a set of 915 Anisakis larvae confirmed the northern stock to be parasitized by A. simplex (s.s.) while off the Iberian Peninsula hake there was a mixed infection pattern with larvae of A. simplex s.s. (67.4% of identified larvae), A. pegreffii (31.9%) and the F1hybrid (0.7%). The observed burden of Anisakis spp. larvae differed markedly between fishing areas. The presence of very high Anisakis spp. burdens in a comparatively small proportion of individual fish was well-illustrated with characteristic tensegrity grid architecture for parasite aggregation derived from a plaque-forming cell response observed in the abdominal cavity of larger fish specimens. Demographic infection values were remarkably high in Grand Sole and off the Iberian Peninsula, with 100% prevalence and mean abundances in the fillets ranging from 247 (A. simplex) in hake from Grand Sole to 60 A. simplex and 20 A. pegreffii in southern European populations. Infections were less prevalent and less intense in the hake sample from Scottish waters. Fish size was the most important factor affecting Anisakis spp. prevalence and abundance, with larger fish containing more Anisakis larvae. Anisakis abundance within individual fish was also positively correlated with the condition index although this does not rule out negative effects on the host, and with trophic level, even after fish size was accounted for. These results suggest that higher Anisakis burden is associated with a higher food intake and with eating larger prey. The risk profile for zoonotic parasites herein described for European hake populations underlines the urgent need for adopting a contingency plan that minimizes the risk exposure.