Viability of Metagonimus romanicus (Ciurea, 1915) metacercariae after physico-chemical treatments

Digenean (Heterophyidae) trematodes include several zoonotic species such as the genus Metagonimus (Katsurada, 1912). Metagonimus romanicus (Ciurea, 1915) is a species widely distributed in Europe, whose metacercariae can be found on cyprinoids from the River Danube in Hungary. The aim of the study was to measure the viability of Metagonimus romanicus metacercariae by physical (freezing, heating, desiccation) and chemical (acetic acid and NaCl solutions) treatments. The methods were chosen as a model for procedures commonly used in traditional food preservation (such as freezing, salting, pickling and smoking) to measure the survival rate of metacercariae under different conditions. Most physical treatments (freezing of metacercariae at −20 °C, keeping them at 40 °C and 60 °C and desiccation) and chemical treatments (2.5%, 5%, 10% acetic acid solution and 5% and 10% NaCl solution) killed the metacercariae in a relatively short time (from 30 min to 6 days depending on the treatment) so their effects eliminated the risk of zoonotic infection. On the other hand, the metacercariae survived at room temperature and at 4 °C up to one month. Therefore, storing unprepared fish in domestic refrigerators cannot prevent infection with metacercariae in humans.