Necessity of adaptation of RNA viruses in host switching events between taxonomically distant reservoir animals

点击翻译按钮获取中文摘要

The majority of emerging infectious diseases are caused by zoonotic RNA viruses often transmitted by bats, rodents and birds. Their high mutation rate allows fast adaptation to novel species increasing the risk for zoonotic host transitions. Host defense mechanisms like the innate immune response are conserved among higher vertebrates and represent a major obstacle that viruses have to overcome. The interferon (IFN) system as part of the innate immune response is among the first and most effective antiviral defense mechanisms and viruses have evolved efficient countermeasures (IFN antagonists) to inhibit the induction and signaling of IFN. It can thus be assumed that the IFN system is fate-determining for viral host switching events.The aim of the proposed project is to analyze if the necessity for viruses to adapt during host transition correlates on a quantitative scale with the phylogenetic distance between hosts of interest. We will focus our study on the ability of viruses to antagonize the species-specific IFN induction pathway of different hosts. To this end we want to quantify the activity of known viral anti- IFN proteins of six selected viruses (SARS-Coronavirus, Ebola-, Nipah-, Rabies-, Hanta- and Influenza A virus) in cell cultures from 12 different mammalian/avian species. This will be done by overexpressing the antagonists in the respective cell cultures followed by stimulation of the IFN induction. Cell cultures from the predicted natural hosts will be used as reference. The IFN mRNA expression will be measured by species-specific real-time RT-PCRs. The IFN secretion will be determined by an established calibrated pan-species vesicular stomatitis virus-based bioassay. Quantitative outcomes of the in-vitro IFN experiments will be directly correlated with inter-host patristic distances based on different gene clusters. The latter shall be expressed along single and concatenated gene trees calculated by ML- and Bayesian methods. Since we are interested in innate immune responses we will also include genes and promoters specifically involved in the IFN response.As a long-term goal we want to identify virus family- or inter-host distance-specific patterns that will facilitate risk assessment of novel reservoir-borne viruses immediately as they are being detected.