Vector competence: The role of viral proteins in transmission of bluetongue virus by midges

Authors: VAN RIJN, PIET - Wageningen University; Drolet, Barbara; ROOST, ASHLEY - Wageningen University; BONSTRA, JAN - Wageningen University; VAN GENNIP, RENE - Wageningen University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/4/2018
Publication Date: 8/27/2018
Citation: Van Rijn, P., Drolet, B.S., Roost, A., Bonstra, J., Van Gennip, R. 2018. Vector competence: The role of viral proteins in transmission of bluetongue virus by midges. Meeting Abstract. 1:1.

Interpretive Summary:

Technical Abstract: Transmission of vector-borne virus by insects is a complex mechanism consisting of many different processes, such as viremia in the host, uptake, infection, replication and dissemination in the vector, and delivery of virus to susceptible hosts leading to viremia. All these processes must be sufficient to maintain virus circulation. In addition, transmission efficiency of virus is strongly influenced by many factors such as temperature and the environmental condition. Bluetongue virus (BTV) is the prototype vector-borne orbivirus. Conventionally, BTV serotypes 1-24 are spread competent biting Culicoides midges (typical BTVs). New serotypes 25-29 were discovered in goats, and belong to a group of atypical BTVs with specific characteristics, including lack of virus growth on Culicoides (KC) cells (Batten et al., 2012; Breard et al., 2017; Chaignat et al., 2010). Extensive studies have shown that most reassortants of BTV1 and 26 replicated well in both mammalian (BSR) and Culicoides (KC) cells, whereas some reassortants did not replicate in KC cells (Pullinger et al., 2016). Apparently, RNA dependent RNA polymerase VP1, subcore protein VP3, and outer shell proteins VP2 and VP5 are involved in ‘differential virus replication’. Previously, we demonstrated uptake by, and replication of, BTV11 in competent Culicoides sonorensis midges, and preliminary studies showed the role of several viral proteins in virus propagation in midges (Feenstra et al., 2015). Here, we generated ‘synthetic’ BTV11 aiming to rescue BTV11-based mutants. As expected, replication of BTV11 expressing VP126 was strongly inhibited in KC cells, whereas BTV11 variants expressing different 11/26 chimeric VP1 proteins replicated well in both cell types. Some BTVs infect competent midges only after intrathoracic inoculation (Feenstra et al., 2015), indicating that these viruses cannot escape the midgut barrier following ingestion. Regarding vector competence, we investigated virus replication in midges after blood feeding, including uptake, replication, and dissemination to the head. The minimal virus dose resulting in 50% infected midges (Midge Alimentary Infective Dose (MAID50)) was +15 TCID50 of BTV11 in competent C. sonorensis midges. This corresponded to +5x105 TCID50/ml BTV11 1:1 diluted in blood, whereas a 20x higher virus titre in fed blood resulted in close to100% BTV11 infected midges. The midge feeding model is useful to study the role of viral proteins in virus replication in vivo. Current findings indicate that several viral genes are involved in differential virus replication in vitro and in vivo. Future research will focus on viral factors associated with vector competence.