A mini review of Tilapia Lake Virus (TiLV): Disease pathogenesis and host immune response against virus

The use of tilapia for farming is increasing every year to meet the worldwide demand for protein sources. Unexpectedly, high mortality rates of tilapia, known as tilapia lake virus (TiLV), have been observed in various countries, including India. TiLV is a pathogenic virus with a trilaminar capsid that is composed of a negative- sense icosahedral RNA virus. Infected tilapia exhibit noticeable signs and symptoms, indicating the presence of the disease. Understanding TiLV is crucial for effective preventing of its spread in the tilapia farming industry. Interferons can hinder viral particles by inhibiting viral replication in the host. These bony fish species require type I and III interferons to protect against the virus. Type I interferons act against all nucleated cells, while type III interferons specifically target dendritic and epithelial cells. Interferon- stimulating gene (ISG) expression, induced by signaling molecules, blocks the virus from spreading to other cells. In vertebrates, the type I IFN-inducible gene product 'Mx' has demonstrated high resistance to orthomyxovirus infection. Recent findings suggest that TiLV lacks HA ligands for binding to the Sia receptor. Protein kinase (PKR), an integral component of the innate immune response, is considered the first-line defense molecule against viral infection in fish. When the viral pathogen enters the host cell, PKR is activated by dsRNA and phosphorylates the translation initiation n factor eIF2 alpha, triggering an innate immune response activated by type I interferon. The host immune response to pathogens is also regulated by cytokines which effectively induce inflammation during TiLV infection. Recent research has shown that intraperitoneally injected zebrafish are susceptible to TiLV infection. Therefore, zebrafish were chosen as a model organism for studying the immune response against TiLV. Zebrafish possess a well-developed immune system that allows for the study of both innate and humoral immunity, providing insights into the antiviral activity of both the host and the pathogen. There is limited understanding of the structure of the virus and minimal information on the immunopathogenesis of TiLV. Therefore, a comprehensive understanding of disease strategies is necessary to develop solution to this epidemic.