Ranavirus frog virus 3 infection in Nile tilapia: evidence of pathogenesis and host susceptibility

Ranaviruses, from the Iridoviridae family, are globally distributed viruses that infect ectothermic vertebrates and cause significant harm to infected animals. The Nile tilapia (Oreochromis niloticus), crucial in global aquaculture, is susceptible to these viruses, particularly the frog virus 3 (FV3) species. The study investigated FV3 pathogenesis in this fish over a 60-day period, revealing the presence of inclusion bodies in different tissues, characteristic of FV3 infection. Macroscopic alterations were observed in infected fishes, including collapsed eyeballs showing edema, white spots on the liver, pale liver, submandibular erythema, dark pigmentation, reddish streaks, varying degrees of exophthalmos, and ascites with accumulation of proteinaceous fluid. Histopathological examinations revealed acute pancreatitis, hepatitis with necrotic areas, vacuolated and hyalinized renal tubules, necrotic and desquamative enteritis, melanomacrophage presence, inflammatory cell accumulation in the liver and pancreas, autolysis in areas of the intestine and pancreas, hemorrhagic vacuolated tubular areas, dissociated heart fibers, myocarditis, and cytoplasmic rarefaction. There was a statistically significant interaction (concentration/day) for hepatosomatic (p < 0.01) and splenosomatic (p < 0.05) indexes in animals infected with FV3. This study contributes to a better understanding of FV3 infection in Nile tilapia and raises the alarm that these fishes may host and consequently disseminate these viruses.