Pathogenesis and complete genome sequence of Decapod iridescent virus 1 (DIV1) associated with mass mortality in Macrobrachium rosenbergii

The pathogen that caused the mass mortalities of Macrobrachium rosenbergii in many farms in Yangzhou, China from June to September 2021, was isolated from diseased prawns and identified as Decapod iridescent virus 1 (DIV1) by molecular diagnostics, phylogenetic analysis, transmission electron microscopy (TEM) observation, virulence test, and histopathological examination, which was named as DIV1-mr. The diseased prawns M. rosenbergii showed symptoms such as white spots under the carapace at the base of rostrum, redness of the hepatopancreas, and empty stomach and intestine. Histopathological observation revealed that the hepatopancreas, gills and intestines of the diseased prawns were severely damaged. Observation of TEM showed that the diseased prawns tissue contained a large number of icosahedral virus particles, which arranged regularly and neatly, and the virus were 175.5 ± 10.6 nm vertex to vertex, 166.6 ± 5.8 nm from face to face, with a nucleoid at 97.6 ± 2.4 nm. The amino acid sequence of the ATPase of DIV1-mr is 100% homologous to that of Cherax quadricarinatus iridovirus (CQIV) and shrimp hemocyte iridescent virus (SHIV). The pathogenicity of DIV1-mr was determined by challenge experiments, and the median lethal dosage (LD50) of DIV1-mr for M. rosenbergii was calculated as 3.28 × 105 copies/mL. Viral metagenomics sequencing showed that the complete genome of DIV1-mr was 167,330 bp in length with 34.57% G + C content. It contains 181 predicted ORFs, which were associated with functional proteins. The study revealed that DIV1 was pathogen causing mass mortality of M. rosenbergii, which will contribute to the in-depth study of the epidemiological investigation, and pathogenic mechanism of DIV1 at the molecular level.