Most common fish viral diseases

Definition:

It is highly contagious viral disease of salmonid fish especially fry and fingerlings characterized clinically by high mortality rate, abnormal swimming behaviors and pancreatic necrosis.

Etiology:

Infectious pancreatic necrosis virus (IPNV) has hexagonal profile without envelopes and a diameter approximately 60 nm in diameter whose genome is bi-segmented double-stranded RNA (dsRNA) belonging to Aquabirnavirus subgroup of the Birnaviridae (Munro & Midtlyng, 2011).

Mode of Transmission:

The virus is efficiently transmitted horizontally through cohabitation with infected fish and vertically by shedding virus via eggs.

Infection survivors act as asymptomatic carriers shed virus into water for years, serving as reservoirs and disseminating it through water via feces, particularly during stress, and the breeders through their reproductive products (Reno, 1999).

 Salmonids are highly susceptible - other fish species like common carp and tilapia are affected and serve as asymptomatic carriers.

Clinical signs: Abnormal swimming behavior Anorexia, Darkened skin. Exophthalmia, Hemorrhages in the ventral surfaces and Abdominal distension. High mortality reached 100% in fry and young fingerlings. 

PM lesions:

 Congestion and hemorrhagic areas in the pancreas, intestine and stomach. Abnormal pale gills, spleen and liver and ascetic fluid in the abdominal cavity.

Histopathological lesions:

Necrosis, Vacuolation and Pyknotic nuclei in liver cells.

Necrosis of the pancreatic acinar cells and inflammatory infiltration early stage.

Necrosis in the hematopoietic tissues of the kidney and spleen.

Desquamation and sloughing of intestinal mucosa.