Systemic infection of Prohemistomum vivax and Cyanodiplostomum encysted metacercariae in African catfish (Clarias gariepinus) from a heavily polluted drain at Giza, Egypt: morphological, molecular and histopathological study.

Aquatic environmental pollution could be a direct trigger of infection through cercarial invasion to skin / gills or indirectly as a predisposing factor that damage the physical barriers of targeted fish resulting in high intensities of EMC infections in all fish vital organs. In the current study, a total of 150 African catfish (Clarias gariepinus) were randomly collected from Mariotteya drain all the way through the Egyptian township of Shabramant located at the historical heart of Giza. Catfish samples were collected in mid-summer during the period from June to July 2024. A well-documented surge in unionized ammonia, water alkalinity, marked decline in dissolved oxygen together with decreased transparency were signaling a chronic case of agricultural and municipal pollution in which all physical mucosal immunological barriers were harshly suppressed. This environmental disruption has resulted in cellular, biological and pathological alterations in which the invasion of digenean cercariae was favored as documented in the histopathological sections made from affected tissues. Parasitological examination revealed the presence of two distinct EMC belonging to Prohemistomum vivax and Cyanodiplostomum spp. which were presumptively identified using the regular morpho-taxonomical methods and confirmed utilizing the sequencing of the ITS2 rDNA gene which is considered good marker in the differentiation between the digenean species and the phylogeny analysis. Histopathological examination of sampled fish tissues has revealed that EMC infection was not only limited to fish musculatures, yet it extends to internal organs including spleen and kidney to present a unique form of systemic EMC infection. EMC were documented within the splenic & renal tissues with remarkable activation of melanomacrophage centers (MMC) denoting the pathophysiological response of hematopoietic tissues to the EMC invasion. The current study sheds light on the growing danger of aquatic pollution and its direct trigger of zoonotic metacercarial spread through the consumption of infected fish flesh.