Effect of different temperatures on viability of seven encysted metacercariae recovered from freshwater fishes in Qualyobia, Egypt

ABSTRACT

Encysted metacercariae [EMC] from seven trematod-zoonotic parasites were exposed to different temperature mechanisms. Boiling of the infected fishes was sufficient to kill the EMC, frying of fishes for five minutes was quite sufficient to inhibit the viability of EMC, but frying for 10 minutes killed all EMC. Grilling of infected Tilapia zillii was sufficient to kill EMC after 10 minutes; however five minutes were sufficient only to kill EMC in Clarias gariepinus. Regarding chilling at 5°C, T. zillii EMC showed variation in response. Complete loss of viability of Prohemistomatidae EMC was achieved after 14 days, for Haplorchidae after 11 days, for Diplostomatidae after 12 days, while Clinostomatidae EMC required 15 days. For Cl. gariepinus, Bagrus bajad and Chrysichthys auratus achieved results were similar to those for T. zillii but with fewer days of withstanding chilling. The EMC infecting Tilapia lost their viability by freezing at -5 °C and -10 °C for Prohemistomatidae after 48 and 40 hours, for Diplostomatidae after 24 and 16 hours and for Clinostomatidae cysts after 48 and 32 hours respectively. In infected Clarias gariepinus, Bagrus bajad and Chrysichthys auratus the EMC lost their viability by fireezing at -5 °C and -10 °C for periods shorter than those of Tilapia sp