Non-essential viral proteins of orbiviruses are essential for vector-borne spread by midges

Authors: VAN RIJN, PIET - Utrecht University; FEENSTRA, FEMKE - Utrecht University; POTGIETER, CHRISTIAAN - Utrecht University; Drolet, Barbara; VAN DE WATER, SANDRA G.P. - Utrecht University; VAN GENNIP, RENE G.P. - Utrecht University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 1/27/2017
Publication Date: 3/31/2017
Citation: Van Rijn, P.A., Feenstra, F., Potgieter, C., Drolet, B.S., Van De Water, S., Van Gennip, R. 2017. Non-essential viral proteins of orbiviruses are essential for vector-borne spread by midges. Meeting Abstract. 1: 1-1.

Interpretive Summary:

Technical Abstract: Members of the Reoviridae family are non-enveloped multi-layered viruses with a double stranded RNA genome consisting of 9-12 genome segments. The Orbivirus genus contains vector borne virus species with 10 genome segments such as bluetongue virus (BTV) with about 30 serotypes, and African horse sickness virus (AHSV) with nine serotypes. BT and AHS are listed animal diseases and have a huge socio-economic impact. Non-structural proteins NS1-NS4 of BTV are not required for reconstitution in vitro, and purified cores particles - without outer capsid proteins VP2 and VP5 - are highly infective. We used reverse genetics to demonstrate that NS3 and NS4 are not required for rescue of BTV and AHSV. NS3 deletion orbiviruses are novel vaccines named Disabled Infectious Single Animal (DISA) vaccines. The prototype BT DISA vaccine is protective, non-pathogenic, and enables differentiation of infected from vaccinated animals (DIVA principle). Moreover, the BT DISA vaccine platform is applicable for many BTV serotypes by VP2 exchange. Above all, DISA vaccine virus is non-transmittable on two levels (DISA principle): no viremia after vaccination and no propagation of DISA vaccine virus in midges after injection blocks vector-borne transmission. Initial studies on AHS DISA vaccine are in progress, including the use of AHS DISA vaccine platform for rescue of variants for all nine AHSV serotypes by VP2 exchange. In these studies, we showed that structural protein VP2 is not essential for virus replication in mammalian cells. However, virus release is completely blocked in KC cells, a cell line derived from larvae of Culicoides midges. We conclude that both NS3 and VP2 are essential for virus propagation in competent Culicoides sonorensis. Apparently, NS3- mediated release of orbiviruses is essential for pathogenicity/virulence and viremia in the host and for virus propagation in the competent insect vector.