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

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.