Vector competence of European mosquitoes to Rift Valley fever virus

RVFV is an arbovirus readily transmitted through several mosquito genera including Aedes and Culex
mosquito vectors, and has a large host range. The recent expansion of the geographical range of RVFV
clearly indicates that RVFV is not restricted to Africa. It has been proposed that a single infected person
or animal that enters a naive country is sufficient to initiate an outbreak. This transmission scenario is
becoming more probable due to the expansion of worldwide trade and travel. The objectives of this
Emida project, RiftVectors, will be to understand the biology of natural RVFV vectors and their counterparts in
Europe as an indicator for assessing the risk of RVFV to be established in Europe.
Within this Emida project, we will further analyze, and develop new methods to distinguish mosquito vector and
potential vector species, and analyze whether they can transmit RVFV- especially european mosquitoes which
may be able to transmit RVFV. We will also analyze how the immune system of mosquito vectors can control RVFV
infection, and how this relates to whether mosquitoes can transmit RVFV or whether novel antiviral targets
can be discovered. Interestingy, endosymbiotic Wolbachia bacteria of insects now are widely used in symbiosis-based
control strategies against arboviruses. We will analyze what the effect of Wolbachia on the vector competence of mosquitoes
to RVFV will be, and if this could be used as a control strategy against this virus.
Our international consortium of partners has the expertise to tackle these questions on the
vectors of RVFV. We expect that our results will improve assessments of when and which
mosquito species could spread RVFV, and we aim to identify novel ways of controlling
RVFV emergence.

This Emida project, RiftVectors, will address topics relating to arthropod vectors of RVFV. Firstly, we will improve methods for identification of RVFV vectors (with special focus on European counterparts of tropical mosquito species) through the use of molecular tools, and the
provision of quantitative estimates of species dynamics in European areas with potential RVFV vectors. Secondly, we aim to gain further insights into the competence of potential RVFV vectors, especially that of potential European vectors in comparison to their African counterparts; we will experimentally asses whether RVFV can adapt to European mosquitoes, and determine environmental factors influencing
maintenance and vertical transmission. Thirdly, we will study the induction and nature of innate immune responses of RVFV vectors, followed
by investigations on how these host responses control RVFV replication. Finally, we will carry out a detailed investigation whether, and if so how, Wolbachia bacteria can be used to inhibit RVFV replication and transmission in vector mosquitoes, as has been shown for other
arboviruses.

These questions will be addressed by five work packages. Two partners will be based in the UK (University of Oxford, MRC-University of Glasgow Centre for Virus Research).

RVFV is an arbovirus maintained within an enzootic cycle between zoophilic mosquitoes and a variety of wild animals. Infection
causes severe and often fatal illness in sheep and cattle. RVFV has been isolated from at least
30 mosquito species, mostly Aedes and Culex. The probability of RVFV emerging in virgin
areas is likely to be increasing. This could involve territories near or within Europe, as well as trading partners.
Besides climate change which could affect the biology of vectors and their geographical distribution, increases of
international trade of livestock and human movements could lead to the introduction of RVFV in regions where susceptible hosts
and suitable vector mosquitoes reside. Indeed, the geographical range of RVFV has extended
over the past 10 years. More than 30 mosquito species have been found to be naturally
infected by RVFV including Aedes, Anopheles, Culex, Eretmapodites and Mansonia, and by
other vectors including sand flies. It has been proposed that a single infected person or
animal (live or dead) that enters a naive country is sufficient for the initiation of a major
outbreak before RVFV would ever be detected. This would have a major impact on animal and public health.
The biology of RVFV/vector interactions as well as the biology of vectors and potential RVFV vectors are poorly
understood and more research in this area is required to inform policy,
assess risk and develop novel control strategies.