Development of reverse genetics systems and investigation of host response antagonism and reassortment potential for Cache Valley and Kairi viruses, two emerging orthobunyaviruses of the Americas.

James I Dunlop,Sejal Modha,Dana L Vanlandingham,Aitor Navarro,Ping Li,Alain Kohl,Lily Tong,Joseph Hughes,Richard M Elliott,Ana Da Silva Filipe,Daniel Mair,Gavin S Wilkie,Stephen Higgs,Yan-Jang S Huang,Benjamin Brennan,Agnieszka M Szemiel,Vattipally B Sreenu,Gregory D Ebel

doi:10.1371/journal.pntd.0006884

Abstract

Orthobunyaviruses such as Cache Valley virus (CVV) and Kairi virus (KRIV) are important animal pathogens. Periodic outbreaks of CVV have resulted in the significant loss of lambs on North American farms, whilst KRIV has mainly been detected in South and Central America with little overlap in geographical range. Vaccines or treatments for these viruses are unavailable. One approach to develop novel vaccine candidates is based on the use of reverse genetics to produce attenuated viruses that elicit immune responses but cannot revert to full virulence. The full genomes of both viruses were sequenced to obtain up to date genome sequence information. Following sequencing, minigenome systems and reverse genetics systems for both CVV and KRIV were developed. Both CVV and KRIV showed a wide in vitro cell host range, with BHK-21 cells a suitable host cell line for virus propagation and titration. To develop attenuated viruses, the open reading frames of the NSs proteins were disrupted. The recombinant viruses with no NSs protein expression induced the production of type I interferon (IFN), indicating that for both viruses NSs functions as an IFN antagonist and that such attenuated viruses could form the basis for attenuated viral vaccines. To assess the potential for reassortment between CVV and KRIV, which could be relevant during vaccination campaigns in areas of overlap, we attempted to produce M segment reassortants by reverse genetics. We were unable to obtain such viruses, suggesting that it is an unlikely event.

Highlights

The bunyaviruses are a large grouping of animal and plant-infecting viruses with a segmented, negative-stranded genome
Replication studies in IFN producing cell lines showed slower growth of the NSs-deletion carrying viruses compared to wild type virus
We demonstrated using genetic studies that Cache Valley virus (CVV) and Kairi virus (KRIV) are unlikely to combine by reassortment to form novel viruses at least for one combination tested here, and propose that such recombinant viruses would be suitable live attenuated vaccine candidates

Summary

Introduction

The bunyaviruses are a large grouping of animal and plant-infecting viruses with a segmented, negative-stranded genome. The order Bunyavirales was recently proposed to include ‘bunyavirus like’ viruses that could not be assigned to the previous 5 genera (https://talk.ictvonline.org/ taxonomy/) [1] This has resulted in the following new families: Feraviridae, Fimoviridae, Hantaviridae, Jonviridae, Nairoviridae, Phasmaviridae, Phenuiviridae and Tospoviridae; the remaining Peribunyaviridae family, previously called Bunyaviridae, contains the previous Orthobunyavirus genus which includes Cache Valley and Kairi viruses (CVV and KRIV, respectively). KRIV, like CVV, belongs to the Bunyamwera serogroup It is another example of a potentially emerging virus of the Americas and was first isolated from various mosquito species in Trinidad including Aedes, Wyeomia, Culex and Psorophora ssp. KRIV does not cause any documented clinical disease symptoms in humans or animals

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