Genetic characterisation of an Iflavirus associated with a vomiting disease in the Indian tropical tasar silkworm, Antheraea mylitta

Antheraea mylitta, the Tropical tasar silkworm, is frequently affected by a vomiting disease called Virosis by sericulturists although not confirmed being of viral origin. Based on the symptoms and the disease pattern, the causal agent is however suspected to be a virus. The condition involves a series of characteristic and progressive symptoms that generally culminates in the death of the larva. The disease is common in autumn season (SepOct), with widespread distribution causing severe damage to the tasar silk industry. The leads for this study were obtained from a transcript identified in the EST database in a different study, which matched the positive strand of Iflavirus, an RNA virus known to infect insects. In the present study the genome of this novel Iflavirus was characterised and the full length of the genome was found to be 9728 nucleotides long encoding for a single large open reading frame (ORF) with flanking NTR regions at 5 ' and 3 ' ends and a natural poly A tail at the 3 ' end. The ORF encoded structural proteins at the N-terminal end and non-structural proteins at the C-terminal end with a predicted 2967 amino acid long polyprotein. The structural proteins consisted of 4 proteins (VP1-VP4) and the non-structural proteins consisted of helicase, RNA-dependent RNA polymerase and 3C-protease. The virus is found in various tissues (midgut, fatbody, trachea, Malpighian tubules and silk gland) and also has a vertical route of transmission, i.e., from gravid females to the offspring. Based on the available data, the virus is a new member of Iflaviridae for which we propose the name Antheraea mylitta Iflavirus (AmIV).