Prevalence, Morphological, and Molecular Diagnosis of Some Foodborne Encysted Metacercariae Affecting Fish and Their Control Using Some Food Safety Measures

A total of 100 Oreochromis niloticus, 100 Clarias gariepinus and 100 Mugil capito of variable weights and lengths were collected from Suez and Ismailia governorates from early August 2022 to late July 2023 to detect the total and seasonal prevalence of encysted metacercariae and their distribution in different fish body parts and organs. The total prevalence of encysted metacercariae (EMC) in O. niloticus was 84.15%, the highest prevalence was in the muscles of the tail region (95.9%), followed by the trunk region (74.5%) and the head region (54.8%). Among C. gariepinus, it was 99.0% in trunk regions, 89.65% in the head region and 82.3% in the tail region. In Mugil capito, the highest was in the trunk region (93.9%), followed by the head region (66.95%) and the tail region (57.75%). Seasonally, the highest prevalence was recorded in winter and summer; 100.0 and 88.3% for O. niloticus and M. capito, respectively. While in C. gariepinus, there was no significant difference of prevalence between all seasons as it was 86.65, 85.0, 85.0 and 83.3 in autumn, summer, winter, and spring, respectively. The recovered EMC from O. niloticus and C. gariepinus were morphologically and molecularly (PCR) identified to belong to family Cyathocotylidae. These EMC were successfully advanced into adult worms after the experimental infection of Wister albino rats. The developing adult flukes were Prohemistomum vivax, Mesostephanus appendiculatus and Mesostephanus fajardensis,which are of public health importance. Freezing the infected muscles of O. niloticus and C. gariepinus with EMC at -17 to -15°C for 3 to 7 days was sufficient to destroy all EMC in these fish muscles. Cooking using an electric oven at 250°C for 15- 20min was sufficient only to destroy EMC in O. niloticus muscles. Controlling EMC using processing methods such as freezing and cooking was very important to avoid zoonosis and ensure food safety.