Drivers of helminth infections and associated risk factors in ommastrephid squids in the Mediterranean Sea with a focus on the zoonotic nematode Anisakis pegreffii (Anisakidae)

In marine ecosystems, squids represent the trophic bridge for many heteroxenous helminth parasites, being cestodes and nematodes the most prevalent. Here, we investigated the drivers of helminth infections in the broadtail shortfin squid, Illex coindetii (Ommastrephidae), focusing on the zoonotic nematode Anisakis pegreffii, in the Ionian Sea (Southern Italy). Additionally, a less common ommastrephid squid, the flying squid Todaropsis eblanae, often fished and mixed along I. coindetii was also examined. Parasites from both squid species were molecularly identified, revealing larvae from three ascaridoid nematode (A. pegreffii, Lappetascaris sp., and Skrjabinisakis physeteris), and two cestode species (Anthobothrium sp. and Heteronybelinia cf. estigmena) in I. coindetii, and two ascaridoid species (A. pegreffii and S. physeteris) in T. eblanae. Anisakis pegreffii was the most prevalent and abundant parasite in both hosts, infecting visceral organs, except for five larvae recovered in the mantle tissue of I. coindetii. In I. coindetii the host size was positively correlated with A. pegreffii abundance, total parasite abundance and species richness, suggesting bioaccumulation over time in older individuals. Parasite abundance, including A. pegreffii, exhibited significant seasonal differences, likely related to host and/or parasite lifestyle or migratory dynamics. The distinctive anatomical allocation of A. pegreffii larvae, predominantly towards the stomach and cavity of I. coindetii, indicates recent infections in these squids. Future studies should unveil more information about the seasonality of parasitic infections in squid hosts, and correlated host and parasite annual habits.