Impact of several control measures on the encysted metacercariae of heterophyids.

Abstract

The present study evaluated the effect of temperature, chemicals and microwave irradiation on the viability and infectivity of encysted metacercariae (EMC) of Pygidiopsis genata in fish. Flesh of infected fish was divided into two groups; control (GI) and experimental (GII). GII was subdivided into IIa: exposed to -4 degrees C & -20 degrees C for different periods, IIb: marinated in sodium chloride, acetic and citric acid at different concentrations and exposure times and IIc: subjected to microwave irradiation for 20 seconds. Assessment of the effect of these factors was by studying the viability and infectivity of EMC after isolation from the fish. The ultrastructure change was studied by scanning electron microscope (SEM), in comparison with control. The results showed that the highest significant reduction in the EMC viability and infectivity was detected in those exposed to microwave irradiation (100%). SEM examination showed distortion in the shape of microwave-treated EMC with change in the surface nature. Freezing of EMC at -4 degrees C & -20 degrees C for 10 days at either temperature was sufficient to abolish their infectivity, although some were remained viable. Soaking of flesh in salt or acids reduced EMC viability and infectivity. So, microwave irradiation proved prophylactic for EMC.