Impaired Geotaxis as a Novel Phenotype of Nora Virus Infection of Drosophila melanogaster

Abstract

Nora virus (NV) is a picorna-like virus that contains a positive-sense, single-stranded RNA genome. The virus infects Drosophila melanogaster with no known characterized phenotype. In this study, geotaxis assays and longevity analyses were used to determine if Nora virus infection affects D. melanogaster’s locomotor ability. In addition, Drosophila C virus (DCV), a well-characterized D. melanogaster virus, was used as a positive control, as it has previously shown a locomotor defect in infected flies. Stocks infected with NV (NV+) and DCV (DCV+) and virus-free (NV-/DCV-) stocks were established. Over a 3-year period, approximately 2,500 virgin female flies were tested for geotaxis and longevity using Kaplan–Meier analyses, as well as the Cox Proportional Hazards regression for survivorship. There was a significant decrease in the geotaxis when the D. melanogaster flies were infected with Nora virus compared to uninfected controls, but no difference was found between DCV+ and NV+ trials. There were not significant differences in longevity between the three groups. This is the first time that a phenotype has been recorded in association with Nora virus infection. Overall, the data demonstrate that geotaxis dysfunction may be a phenotypic hallmark of Nora virus infection.

The Novel Agrotis ipsilon Nora Virus Confers Deleterious Effects to the Fitness of Spodoptera frugiperda (Lepidoptera: Noctuidae)

“…The Drosophila Nora virus is horizontally transmitted through the fecal-oral route, causing mild effects on the fitness of infected flies ( Habayeb et al, 2009a ). A recent study postulated that geotaxis dysfunction is a phenotypic hallmark of Drosophila Nora virus infection, which causes the infected flies to significantly lose their climbing ability ( Rogers et al, 2020 ). Notably, the Nora virus is horizontally and vertically transmitted within H. armigera populations, with unclear pathogenic effects on the infected moths ( Yang et al, 2019 ).…”

Nora Virus VP4b and ORF1 Circulate in Hemolymph of Infected D. melanogaster with Coordinate Expression of Vago and Vir-1

“…Nora virus was previously identified primarily within the gut tissue of infected D. melanogaster [13]. After identifying a locomotor defect in infected D. melanogaster [15], it was hypothesized that Nora virus may circulate to other tissues by way of the hemolymph. Nora virus RNA for the ORF1 gene and capsid protein, VP4b, were found to be present in the hemolymph of infected D. melanogaster both by Western blot and qRT-PCR ( Figure 1).…”

“…Our lab has documented a locomotor defect with persistent Nora virus infection. Infected D. melanogaster are significantly hindered in terms of geotaxis, when compared to their uninfected counterparts [15]. To explain this phenotype, it is proposed that Nora virus-specific molecules, ORF1 and VP4B, are circulating in the hemolymph to the brain.…”

In vitro assembly and evaluation of Nora virus VLPs

“…Nora virus causes a persistent infection in D. melanogaster and is transmitted via the fecal-oral route (Habayeb et al, 2009a, Habayeb et al, 2009b. It is postulated that there are no known detrimental effects to D. melanogaster when retaining this virus, but a defect in geotaxis has recently been found (Rogers et al, 2020). Some human Picornaviridae viruses, like poliovirus and coxsackievirus, are able to cause persistent infections that eventually lead to severe health complications (Klingel et al 1992;Rueckert, 1996).…”