title: Early pathogenesis of Autographa californica multiple nucleopolyhedrovirus and Helicoverpa zea single nucleopolyhedrovirus in Heliothis virescens: a comparison of the 'M' and 'S' strategies for establishing fatal infection.
abstract: Nucleopolyhedroviruses (NPVs) (Baculoviridae) produce fatal infections in larval lepidopteran insects. NPVs are designated SNPVs or MNPVs based on whether the occlusion-derived virus (ODV) that initiates primary midgut infections contains single (S) or multiple (M) nucleocapsids. The principal consequence of this ODV packaging is that primary target cells infected with the M phenotype receive multiple nucleocapsids, whereas those infected by the S phenotype receive only one. To determine the biological significance of this difference in the initial infection strategy, a comparison of the primary and secondary infection patterns of the recombinants Helicoverpa zea SNPV (HzSNPV-hsp70/lacZ) and Autographa californica MNPV (AcMNPV-hsp70/lacZ) in orally inoculated larvae of Heliothis virescens was carried out. At dosages yielding similar final mortalities ( approximately 85 %), primary midgut infections by HzSNPV-hsp70/lacZ (indicated by lacZ expression) were observed 6 h earlier and in greater numbers than those generated by AcMNPV-hsp70/lacZ. Infection of secondary target cells in the tracheal epidermis, however, occurred at the same time and at the same rate for both NPVs. A 2 h delay was observed between the onset of primary and secondary AcMNPV-hsp70/lacZ infection, supporting the hypothesis that early tracheal infections were initiated by ODV nucleocapsids repackaged as budded virus. In contrast, an 8 h delay was observed with HzSNPV-hsp70/lacZ, suggesting that systemic infections were established only after virus replication in primary targets. Significant numbers of both MNPV- and SNPV-infected primary target cells were sloughed from the midgut beginning as early as 16 h post-infection. Midgut cell sloughing may be an important host-mediated selection pressure influencing the evolution of NPV morphology and gene regulation, shaping, in part, baculovirus infection strategies.
authors.affiliation: Department of Plant and Microbial Biology, 251 Koshland Hall, University of California, Berkeley, CA 94720-3102, USA.
authors.forename: Jan O
authors.initials: JO
authors.lastname: Washburn
authors.affiliation: Department of Plant and Microbial Biology, 251 Koshland Hall, University of California, Berkeley, CA 94720-3102, USA.
authors.forename: Dominique
authors.initials: D
authors.lastname: Trudeau
authors.affiliation: DuPont Agricultural Products, Stine-Haskell Research Center, PO Box 30, Elkton Road, Newark, DE 19714, USA.
authors.forename: James F
authors.initials: JF
authors.lastname: Wong
authors.affiliation: Department of Plant and Microbial Biology, 251 Koshland Hall, University of California, Berkeley, CA 94720-3102, USA.
authors.forename: Loy E
authors.initials: LE
authors.lastname: Volkman
mesh_terms: D000818:Animals; D000078404:Epidermal Cells; D004817:Epidermis / Q000821:virology; D018840:HSP70 Heat-Shock Proteins; D006434:Hemocytes / Q000821:virology; D007763:Lac Operon; D007814:Larva / Q000821:virology; D007915:Lepidoptera / Q000821:virology*; D019251:Nucleocapsid / Q000378:metabolism; D017924:Nucleopolyhedroviruses / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D011995:Recombination, Genetic; D014132:Trachea / Q000166:cytology / Q000821:virology
chemical_list: D018840:HSP70 Heat-Shock Proteins