Molecular epidemiology of Bombyx mori nucleopolyhedrovirus in Yunnan sericulture region, China

Sericultural production is seriously influenced by the blood pathogens of grasserie, Bombyx mori nucleopolyhedrovirus (BmNPV). To investigate the infectious condition and define an effective control method for BmNPV. 233 from 240 suspected samples infected with BmNPV were detected using PCR identification. One sample was selected from each county in the positive sample collection area, 56 isolates of which were used as experimental objects. The homology of the bro-d nucleotide sequence was at least 91% among the 56 BmNPV isolates. However, the conserved 7 amino acids (percentage of amino acid constant sites, PAACS) at the position 217-224 were absent for YNQJLL001 and YNZTQJ074 pandemic isolates. Phylogenetic tree analysis of bro-d gene separated the BmNPV isolates from Yunnan into 4 main clades: I, II, III, and IV. Clade I was the dominant clade containing 32 local epidemic isolates. Clades II, III, and IV contained 5, 16, and 3 pandemic isolates, respectively. Geographical distribution of clade I in Yunnan showed a concentrated pattern, while the remaining members of the other three clades depicted no direct contact in relation to their locations. This study may provide valuable molecular types on BmNPV isolate distribution in the silkworm-raising regions, also be helpful for evaluating BmNPV pathogenesis and epidemic situations in the Yunnan sericulture region.