Baculoviruses: Molecular Biology of Mosquito Baculoviruses

Baculoviruses found in mosquitoes have been assigned to the nucleopolyhedroviruses and are of growing interest as they may represent a separate branch within the family Baculoviridae that existed prior to the split of lepidopteran nucleopolyhedroviruses and granuloviruses. They may also be ancestral to the baculoviruses from Hymenoptera, which form a branch distinct from the lepidopteran baculoviruses. Mosquitoes are also important vectors of numerous human and veterinary diseases and baculoviruses offer the opportunity to investigate and understand specific virus–host interactions at the molecular level. Mosquito baculoviruses are restricted to larval midgut epithelial cells where development is initiated and completed resulting in death of the mosquito host in 72–96 h. Transmission to the larval host is mediated by divalent cations with magnesium required for transmission while calcium is a potent inhibitor of transmission. Culex nigripalpus nucleopolyhedrovirus (CuniNPV) contains a circular double-stranded DNA genome packaged into rod-shaped singly enveloped nucleocapsids. Complete nucleotide sequencing has determined a genomic size of 108 252 bp encoding at least 109 putative proteins. Striking differences in genome organization, the lack of conservation in gene order, the low level of amino acid conservation for homologous genes, and the absence of many genes that are conserved in other baculoviruses suggest that CuniNPV is a distant relative to lepidopteran and hymenopteran baculoviruses.