African horse sickness virus induces apoptosis in cultured mammalian cells

African horse sickness virus (AHSV) is an arbovirus capable of successfully replicating in both its mammalian host and insect vector. Where mammalian cells show a severe cytopathic effect (CPE) following AHSV infection, insect cells display no CPE. These differences in cell death could be linked to the method of viral release, i.e. lytic or non-lytic, that predominates in a specific cell type. Active release of AHSV, or any related orbivirus, has, however, not yet been documented from insect cells. We applied an integrated microscopy approach to compare the nanomechanical and morphological response of mammalian and insect cells to AHSV infection. Atomic force microscopy revealed plasma membrane destabilization, integrity loss and structural deformation of the entire surface of infected mammalian cells. Infected insect cells, in contrast, showed no morphological differences from mock-infected cells other than an increased incidence of circular cavities present on the cell surface. Transmission electron microscopy imaging identified a novel large vesicle-like compartment within infected insect cells, not present in mammalian cells, containing viral proteins and virus particles. Extracellular clusters of aggregated virus particles were visualized adjacent to infected insect cells with intact plasma membranes. We propose that foreign material is accumulated within these vesicles and that their subsequent fusion with the cell membrane releases entrapped viruses, thereby facilitating a non-lytic virus release mechanism different from the budding previously observed in mammalian cells. This insect cell-specific defence mechanism contributes to the lack of cell damage observed in AHSV-infected insect cells.

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Virus uncoating is required for apoptosis induction in cultured mammalian cells infected with African horse sickness virus

Journal of General Virology ◽

10.1099/vir.0.000124 ◽

2015 ◽

Vol 96 (7) ◽

pp. 1811-1820 ◽

Cited By ~ 4

Author(s):

Elaine Vermaak ◽

Jacques Theron

Keyword(s):

Mammalian Cells ◽

African Horse Sickness ◽

Apoptosis Induction ◽

African Horse Sickness Virus ◽

Virus Uncoating

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VP2 Exchange and NS3/NS3a Deletion in African Horse Sickness Virus (AHSV) in Development of Disabled Infectious Single Animal Vaccine Candidates for AHSV

Journal of Virology ◽

10.1128/jvi.01052-15 ◽

2015 ◽

Vol 89 (17) ◽

pp. 8764-8772 ◽

Cited By ~ 23

Author(s):

Sandra G. P. van de Water ◽

René G. P. van Gennip ◽

Christiaan A. Potgieter ◽

Isabel M. Wright ◽

Piet A. van Rijn

Keyword(s):

Mammalian Cells ◽

Reverse Genetics ◽

African Horse Sickness ◽

African Horse Sickness Virus ◽

Vaccine Platform ◽

Biting Midges ◽

Content Type ◽

Vp2 Protein ◽

Single Animal

ABSTRACTAfrican horse sickness virus (AHSV) is a virus species in the genusOrbivirusof the familyReoviridae. There are nine serotypes of AHSV showing different levels of cross neutralization. AHSV is transmitted by species ofCulicoidesbiting midges and causes African horse sickness (AHS) in equids, with a mortality rate of up to 95% in naive horses. AHS has become a serious threat for countries outside Africa, since endemicCulicoidesspecies in moderate climates appear to be competent vectors for the related bluetongue virus (BTV). To control AHS, live-attenuated vaccines (LAVs) are used in Africa. We used reverse genetics to generate “synthetic” reassortants of AHSV for all nine serotypes by exchange of genome segment 2 (Seg-2). This segment encodes VP2, which is the serotype-determining protein and the dominant target for neutralizing antibodies. Single Seg-2 AHSV reassortants showed similar cytopathogenic effects in mammalian cells but displayed different growth kinetics. Reverse genetics for AHSV was also used to study Seg-10 expressing NS3/NS3a proteins. We demonstrated that NS3/NS3a proteins are not essential for AHSV replicationin vitro. NS3/NS3a of AHSV is, however, involved in the cytopathogenic effect in mammalian cells and is very important for virus release from cultured insect cells in particular. Similar to the concept of the bluetongue disabled infectious single animal (BT DISA) vaccine platform, an AHS DISA vaccine platform lacking NS3/NS3a expression was developed. Using exchange of genome segment 2 encoding VP2 protein (Seg-2[VP2]), we will be able to develop AHS DISA vaccine candidates for all current AHSV serotypes.IMPORTANCEAfrican horse sickness virus is transmitted by species ofCulicoidesbiting midges and causes African horse sickness in equids, with a mortality rate of up to 95% in naive horses. African horse sickness has become a serious threat for countries outside Africa, since endemicCulicoidesspecies in moderate climates are supposed to be competent vectors. By using reverse genetics, viruses of all nine serotypes were constructed by the exchange of Seg-2 expressing the serotype-determining VP2 protein. Furthermore, we demonstrated that the nonstructural protein NS3/NS3a is not essential for virus replicationin vitro. However, the potential spread of the virus by biting midges is supposed to be blocked, since thein vitrorelease of the virus was strongly reduced due to this deletion. VP2 exchange and NS3/NS3a deletion in African horse sickness virus were combined in the concept of a disabled infectious single animal vaccine for all nine serotypes.

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