Localization of tilapia tilapinevirus by in situ hybridization in the brain of nile tilapia (oreochromis niloticus)

Abstract

Tilapia tilapinevirus or tilapia lake virus (TiLV) is an emerging virus that poses a significant negative impact on farmed tilapia globally. Abnormal behaviours such as lethargy, loss of appetite, erratic swimming, stop schooling have been recorded during disease occurrence, which is possibly linked to brain activities. Previous studies described detection of the virus in multiple organs of infected fish; however, little is known about the in-depth localization of the virus in the central nervous system. Herein, we determined the distribution of TiLV and histopathological alterations in the entire brain of Nile tilapia experimentally infected fish. By in situ hybridization (ISH) using TiLV-specific probes, the results indicated that the virus was broadly spread throughout the brain. These findings have supported the association between brain dysfunctions and the neurological manifestation of infected fish. Interestingly, the strongest positive TiLV signal was dominantly detected in the forebrain (function as learning, appetitive behavior, and attention) and the hindbrain (function as controlling locomotion and basal physiology). In addition, the permissive cell zone for viral infection mostly was observed to be along the blood vessels and the ventricles, indicating that the virus may effectively enter the brain through the circulatory system and infect broad regions potentially through the cerebrospinal fluid along the ventricles, and subsequently induce the brain dysfunction. Understanding the pattern of viral localization in the brain may help elucidate the neurological disorders of the diseased fish. Our work revealed the first spatial visualization of viral distribution in the whole infected brain, providing new information on fish-virus interactions and also guide future studies to fulfill the disease pathogenesis.