Prevalence of the broad tapeworm Diphyllobothrium latum in perch (Perca fluviatilis) and analysis of abiotic factors influencing its occurrence in Lake Lario (Como, Italy)

Diphyllobothriosis affects man and mammals as definitive hosts, a well as several fish species as intermediate or paratenic hosts. In Italy, in the last decade, Diphyllobothrium latum (Cestoda, Diphyllobothriidea) has shown a comeback around the shores of Lake Lario (Como), with several cases diagnosed from 2001. Anamnestic data constantly reported the consumption of raw or undercooked fish products in restaurants or local markets. In this study, we carried out a parasitological survey of perch caught in Lake Lario. Between 2005 and 2007, 609 perches (Perca fluviatilis) were sampled from five sites located along the three major branches of the lake and examined for the presence of plerocercoids larvae in the fillets. Data on abiotic factors in the same sampling areas were registered. The mean infection rate of perch was 30%, a value much higher than those observed in other sub-alpine lakes. The data collected indicate that the concentration of total phosphorus could influence the prevalence by D. latum, which seems to be higher in basins with low trophy conditions. Further studies need to be assessed to confirm the relation between prevalence and abiotic factors and to clarify the principal aspects that allow the endemic status of diphyllobothriosis.