Journal
JOURNAL OF GENERAL VIROLOGY
Volume 84, Issue -, Pages 343-351Publisher
MICROBIOLOGY SOC
DOI: 10.1099/vir.0.18701-0
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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//acZ) and Autographa californica MNPV (AcMNPV-hsp70//acZ) in orally inoculated larvae of Heliothis virescens was carried out. At dosages yielding similar final mortalities (similar to85 %), primary midgut infections by HzSNPV-hsp70//acZ (indicated by lacZ expression) were observed 6 h earlier and in greater numbers than those generated by AcMNPV-hsp70//acZ. 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//acZ 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//acZ, 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.
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