Abstract
Baculoviruses are a family of insect-specific pathogenic viruses can persist outside for long periods through the formation of occlusion bodies. In spite of this ability, the UV of sunlight is an essential factor that limits the survival of baculoviruses outside the host. In the current study, we compared the UV tolerance of two strains of Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV), which were isolated in spatially different regions (LdMNPV-27/0 in Western Siberia (Russia) and LdMNPV-45/0 in North America (USA)) and dramatically differ in their potency. We exposed the studied strains to sunlight in an open area for 0.25, 0.5, 1, and 2 hours and later perorally inoculated host larvae with the same doses of virus (5x105) and with doses leading to same effect (LD90). We observed that strain LdMNPV-45/0, which previously showed high virulence against L. dispar larvae, was more sensitive to UV irradiation (estimated as the relative rate of inactivation (r, h -1) and as the half-life of the virus (τ1/2, h)) compared to LdMNPV-27/0. Exposure to sunlight induced a significant delay of LdMNPV-45/0-induced pathogenesis already after 0.25 h of sunlight exposure, while for LdMNPV-27/0 this delay was occurred only after 2 h exposure in spite of used concentrations. We also compared the sequences of the main structural proteins of the studied strains as UV light contributes not only to genome damage in viruses but also to structural protein damage. The most prominent genetic difference between the structural proteins of the strains was related to the loss of the virus enhancin factor-1 (vef-1) gene in the LdMNPV-27/0 strain. Thus initially highly potent viral strain (such as LdMNPV-45/0) is not recommend to use in the regions (or forest stand density) with high UV load. The role of virus enhancin factor-1 in baculovirus tolerance to UV needs for following studies.
Highlights
Baculoviruses are a unique family of viruses that exclusively infect insects and often lead to mass epizootics in host populations [1,2]
The half-life (τ1/2) of the Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV)-27/0 for same impact was longer than for LdMNPV-45/0), but a significant difference was only detected for the same impact (LD90) (Table 1)
Compared to LdMNPV-27/0, the LdMNPV-45/0 strain led to a more rapid death of larvae when applied at the same concentrations; but LdMNPV-27/0 killed larvae faster when equal doses (LD90) were used
Summary
Baculoviruses are a unique family of viruses that exclusively infect insects (according to International Committee of Taxonomy of Viruses) and often lead to mass epizootics in host populations [1,2]. The genes encoding polyhedrin/granulin proteins, major structural components of occlusion bodies, are strongly conserved and are used as a molecular criterion for baculovirus taxonomy [6]. Another feature of baculoviruses (inherent to many other viruses) is the ability to infect the host without a symptomatic appearance [7,8,9,10,11,12,13]. A baculovirus can be transmitted from parents to progeny and is activated by the effects of stress factors on the host organism, leading to its death [14]
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