A Novel Virus Causes Scale Drop Disease in Lates calcarifer

Abstract

From 1992 onwards, outbreaks of a previously unknown illness have been reported in Asian seabass (Lates calcarifer) kept in maricultures in Southeast Asia. The most striking symptom of this emerging disease is the loss of scales. It was referred to as scale drop syndrome, but the etiology remained enigmatic. By using a next-generation virus discovery technique, VIDISCA-454, sequences of an unknown virus were detected in serum of diseased fish. The near complete genome sequence of the virus was determined, which shows a unique genome organization, and low levels of identity to known members of the Iridoviridae. Based on homology of a series of putatively encoded proteins, the virus is a novel member of the Megalocytivirus genus of the Iridoviridae family. The virus was isolated and propagated in cell culture, where it caused a cytopathogenic effect in infected Asian seabass kidney and brain cells. Electron microscopy revealed icosahedral virions of about 140 nm, characteristic for the Iridoviridae. In vitro cultured virus induced scale drop syndrome in Asian seabass in vivo and the virus could be reisolated from these infected fish. These findings show that the virus is the causative agent for the scale drop syndrome, as each of Koch’s postulates is fulfilled. We have named the virus Scale Drop Disease Virus. Vaccines prepared from BEI- and formalin inactivated virus, as well as from E. coli produced major capsid protein provide efficacious protection against scale drop disease.

Detection of infectious spleen and kidney necrosis virus (ISKNV) and turbot reddish body iridovirus (TRBIV) from archival ornamental fish samples

“…In this case, 'Temperomegalocytivirus' could be a suitable name for the species currently represented by TSIV given the temperate origins of the host species of the latter virus. The recently described SDDV from cultured Lates calcarifer (Gibson-Kueh et al 2012, de Groof et al 2015) also demonstrates molecularly phylogenetic affinities with the genus Megalocytivirus, being basal to this group. However, although IBC are present in fish affected with SDDV, they are not as prevalent as in fish typically infected with viruses in the genus Megalocytivirus (Gibson-Kueh et al 2012), and therefore this could represent a transitional form between megalocytiviruses and other iridovirids.…”

“…For the MCP gene, the near complete coding sequence was available for the recently described threespine stickleback iridovirus (TSIV), a more divergent megalocytivirus (Waltzek et al 2012), so all sequences were trimmed to a final length of 1342 nucleotides to enable the MCP gene tree to include TSIV. The tree was then rooted against scale drop disease virus (SDDV), a divergent iridovirid that has affinity with the genus Megalocytivirus (de Groof et al 2015). However, since the GenBank entry for the ATPase gene of TSIV was missing approximately the first 15% of the coding sequence, valuable information would be lost by trimming all sequences to accommodate the TSIV sequence.…”

Mortality from scale drop disease in farmed Lates calcarifer in Southeast Asia

“…Although production is rising, infectious diseases are considered major threats to production (Dong, Jitrakorn et al., ; Ransangan & Manin, ; Sharma, Rathore, Verma, Sadhu, & Philipose, ; Tendencia, ; Toranzo, Magariños, & Romalde, ). One emerging disease in farmed L. calcarifer in Southeast Asia is scale drop disease (SDD) caused by a novel Megalocytivirus (SDDV) (De Groof et al., ; Gibson‐Kueh et al., ). Another is scale drop and muscle necrosis (SDMN) disease associated with a pathogenic Vibrio harveyi isolate (Dong, Taengphu et al., ; Kayansamruaj et al., ).…”

Concurrence of Iridovirus, Polyomavirus, and a Unique Member of a New Group of Fish Papillomaviruses in Lymphocystis Disease-Affected Gilthead Sea Bream

“…Importantly, we have identified a set of at least eight previously undescribed genes, which provide useful markers to analyze the evolutionary relationships within this group. Two of them were found to be most similar to genes from the recently described scale drop disease virus (SDDV), a distant member of the megalocytiviruses infecting tropical fish in Southeast Asia (31). The genomic GC content value of SDDV (37%) is very different from that of other megalocytiviruses (55%) but closer to that of LCDV-Sa (33%), suggesting the existence of a common ancestor for viruses belonging to both genera of fish-infecting iridoviruses.…”