Pathogenicity study of covert mortality nodavirus (CMNV) infection in zebrafish model

Abstract Covert mortality nodavirus (CMNV), a new emerging shrimp virus, was capable of crossing species barriers to infect fish. However, impending studies in elucidating pathogenicity of CMNV in fish have been limiting due to the lack of appropriate animal disease models. An attempt of establishing an in vivo model of CMNV infection in zebrafish (Danio rerio) were conducted in present study. Further, CMNV infection in zebrafish important tissues was also investigated by using the methods of fatality rate statistics, histopathology, in situ hybrization (ISH) and transmission electron microscopy (TEM). Behavioral observations of the infected zebrafish showed that the infected individuals exhibited an abnormal spiraling swimming activity, and some individuals had exceptionally protruding eyes. The eye and brain tissues of artificially infected zebrafish were proved to be CMNV-positive by ISH, and pathological changes like vacuolation of nervous tissue were observed in this two tissues. Analysis of TEM also confirmed masses of CMNV-like virus particles in the brain and eye tissues of the infected zebrafish. CMNV positive signals of ISH were also detected in muscle, intestine and gill tissues, and myolysis in the muscle, dropping of epithelial cells in gill were found in the same site with positive signals. In addition, CMNV could cause 53.33% mortality of zebrafish within 14 days of post challenge injection. The establishment of the zebrafish infection model of CMNV offered a valuable tool for further investigations of the host-virus interactions, especially the underlying molecular mechanisms of CMNV for crossing species barrier to infect fish.