Detection of Iridoviruses in Fishes in Damietta and Sharkia Governorates, Egypt

Abstract

Iridovirus infection has threatened the aquaculture industry worldwide. It has been associated with severe disease and economic losses in fish. In the present study, sixty-two fishes (Sea bream = 50; Sea bass = 3; Mullet = 9) were collected from Damietta and Sharkia Governorates, Egypt during May 2019-September 2020. The clinical signs, gross lesions and histopathological findings were recorded and later confirmed by molecular detection of Iridovirus in different fish species. Besides, isolation of molecularly identified Iridovirus from fish tissues in Vero cell cultures was done. Clinically, the affected fishes become lethargic, exhibit severe anemia, petechiae in the skin and gills. Unilateral hemorrhages in eye and cloudy eye were recorded only in Sea bream fish. Necropsy of the infected fishes revealed congestion of the internal organs, petechial hemorrhages on spleen, liver, kidneys and heart. Necrotic foci on liver were also observed. Histopathological examination revealed congestion of portal veins, cytoplasmic vacuolation with presence of intranuclear eosinophilic inclusion bodies within degenerated hepatocytes. Multifocal necrosis and various degree of inflammation in different fish tissues were observed. Molecularly, the obtained 1000 bp amplicon by PCR confirmed the presence of Iridovirus major capsid protein (MCP) gene with a percentage of 12.1%. It was detected in both fry and market size fish as well as in clinically infected and apparently healthy fish. The molecularly identified virus was able to replicate in Vero cells at 28oC, but not at 37 oC. To our knowledge, this is the first report of Iridovirus isolation in Vero cells and detection in fish within Damietta and Sharkia Governorates, Egypt. Further studies are recommended to investigate its presence on a broader scale with genomic sequence analysis.