Morphological and molecular evidence that Culex nigripalpus baculovirus is an unusual member of the family Baculoviridae

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Abstract
We present evidence that a newly discovered mosquito virus fromCulex nigripalpusis an unusual member of the familyBaculoviridae. Development of this virus was restricted to nuclei of midgut epithelial cells in the gastric caeca and posterior stomach. The globular occlusion bodies were not enveloped, measured around 400 nm in diameter, occurred exclusively in nuclei of infected cells and typically contained four, sometimes up to eight, virions. The developmental sequence involved two virion phenotypes: an occluded form (ODV) that initiated infection in the midgut epithelial cells, and a budded form that spread the infection in the midgut. Each ODV contained one rod-shaped enveloped nucleocapsid (40×200 nm). The double-stranded DNA genome was approximately 105–110 kbp with an estimated GC content of 52%. We have sequenced approximately one-third of the genome and detected 96 putative ORFs of 50 amino acids or more including several genes considered to be unique to baculoviruses. Phylogenetic analysis of the amino acid sequences ofDNApoland p74 placed this virus in a separate clade from the generaNucleopolyhedrovirusandGranulovirus. We provisionally assign this virus in the genusNucleopolyhedrovirus, henceforth abbreviated as CuniNPV (forCulex nigripalpusnucleopolyhedrovirus), and suggest that, awaiting additional data to clarify its taxonomic status, it may be a member of a new genus within the familyBaculoviridae.