Infectious hematopoietic necrosis virus (IHNV) outbreak in farmed rainbow trout in Iran: Viral isolation, pathological findings, molecular confirmation, and genetic analysis.

Infectious hematopoietic necrosis virus (IHNV) is the etiological agent of a contagious disease (IHN) mainly in salmonid fish. In the present study, we isolated and identified IHNV in trout fry from Iranian trout farms with unexplained high mortality in 2016. The affected fry showed cumulative mortality of 90% with the gross pathological signs including exophthalmia and hemorrhage of the eye, skin darkening, abdominal distension, ulceration of the snout, and the visceral pallor and yellowish fluid in the intestine. Histopathological examination revealed marked necrosis in the anterior kidney, liver and spleen with the intracytoplasmic inclusion bodies in the liver sections. Also, intranuclear inclusion body and marginated chromatin were observable in the hematopoietic cells of the kidney. The homogenates tissues of infected fry induced IHNV-positive cytopathic effects (CPE) in EPC cells and confirmed by RT-PCR reactions and sequencing. Phylogenetic analysis revealed the Iranian IHNV isolates belonged to the European (E) genogroup with 100% identity to some Italian isolates. This is the first report of IHNV infection in farmed trout fry in Iran describing the viral isolation, clinical symptoms, histopathological findings, molecular confirmation, and genetic analysis suggestion of the specific country of origin.