Covert virus infections allow for viral persistence without killing the host. These infections result in a major reduction in viral loads relative to overt infections. Covert infections are transmitted vertically from parent to offspring, and are only produced in viruses that are capable of adopting an infection strategy that is less virulent to the host as reproduction is required. The fitness costs of infection on the host need to be as little as possible to ensure host survival and reproduction. Covert baculovirus infections in mass-reared Lepidoptera are ticking bombs, causing few or no symptoms until triggered into an overt lytic state when the host is stressed. In order to manage or remove covert infections from mass-reared populations, the mechanisms involved in establishing and maintaining covert infections need to be elucidated.
The main aim of this project is to unravel the molecular mechanisms underlying maintenance of covert virus infections in insect hosts and to determine the impact of such infections on host fitness and immunity. The interaction between the specialist baculovirus SeMNPV and its host Spodoptera exigua will be used as a model host-viral system. Establishing the mechanism in baculoviruses can lead to further investigations into other virus families to see whether homologous mechanisms exist.
In my project I will focus in understanding the potential role of the RNA interference (RNAi) pathway as determinant of the covert infection. The RNAi response in insects is the primary defence against RNA virus challenge, as well as playing an important role in defence against DNA viruses. Small non-coding RNAs (snRNAs) form the primary components of the RNAi pathway, including short interfering RNAs (siRNAs), piwi-interacting RNAs (piRNAs), and microRNAs (miRNAs). The miRNA pathway is an important factor mediating host-pathogen interactions, and may be involved in establishment and maintenance of covert infections. Viruses have been found to produce miRNAs which play a pivotal role in host-virus interactions, particularly in hi-jacking the host’s immune response to aid viral replication.