Seasonal emergence of benign epidermal tumor in farm-reared adult grass carp (Ctenopharyngodon idella) caused by lymphocystis disease virus at Uttarakhand, India

Abstract

From 2017‐2019, during the winter months (November–January), epidermal papilloma like benign tumor was observed in farm-reared adult grass carp, Ctenopharyngodon idella at the northern part of India. An investigation was undertaken to establish the causative agent of this epizootiology. Based on the clinical signs and ineffectiveness of antibiotics to control this disease, viral infection was suspected. A primer was designed to PCR amplify the partial DNA polymerase gene of lymphocystis disease virus (LCDV) from the tumor of moribund grass carp, which yielded 460 bp amplicon. After sequencing this 460 bp amplicon, the viral agent from the tumor of grass carp was identified as lymphocystis disease virus and given strain designation LRI-18 (Genbank accession number-MK347473). Phylogenetic analysis based on the nucleotide sequence of DNA polymerase gene of LCDV revealed the close association of LCDV LRI-18 to LCDV strain from Israel with 99.0% and 96.5% nucleotide and amino acid sequence identity, respectively. LCDV LRI-18 form single (type A; 0.5–2.0 μm) or multiple (type B; 0.5–2.0 μm) intracytoplasmic inclusion bodies on lymphocystis and erythrocyte cells of infected grass carp. Transmission Electron Microscopy (TEM) of blood revealed the presence of enveloped icosahedral virions of approximately 280 nm in diameter with electron dense core and an outer capsid. Histopathological study of various organs of LCDV infected grass carp revealed extensive hypertrophy and fusion of secondary gill lamellae, focal hemorrhage in the eye, pyknotic nuclei in the liver, inflammation in the myocardium, fused villi of intestine and degeneration of the glomeruli in the kidney. Experimental infection by a dip to grass carp fingerlings (average body weight 4.4 ± 0.9 g) using 0.45 μm filtered LCDV crude suspension did not reproduce the disease, and also no mortality were observed. This is the first report of the occurrence of lymphocystis disease in grass carp in India.