Yellow fever virus (YFV), a Flavivirus transmitted by mosquitoes causes a severe hemorrhagic fever in humans. Despite the availability of a safe and effective vaccine (17D), YFV is still a public health problem in tropical Africa and South America. In the Americas, the massive campaign of mosquito control during the first half of the 20th century led to the eradication of Aedes aegypti from most American countries, and as a consequence, urban outbreaks of YF were no longer observed. However, the relaxation of vector control led to the reinfestation of urban areas by Ae. aegypti and the subsequent establishment of the Asian tiger mosquito Aedes albopictus. In Brazil, while human cases are sporadically detected in the Amazonian basin where sylvatic YFV strains circulate between non-human primates and arboreal canopy-dwelling mosquitoes (Haemagogus sp.), they are increasingly reported outside the jungle moving towards the Atlantic coast, the most populated area. In the absence of routine immunization programs, YF may come back in the American towns as it was in the past. The causes leading to the current YF resurgence are multifactorial. From a mosquito vector viewpoint, changes in vector densities, distribution, vector competence or vector as a site of selection for epidemic YFV strains, can be regarded as critical factors. Our project aims to address the contribution of the invasive mosquito Ae. albopictus as a missing link to allow a selvatic YF strain (1D) to become adapted for a transmission in urban areas by the human-biting mosquito, Ae. aegypti. It will be done through three specific objectives: (i) identify Ae. albopictus-adaptive mutations after serial cycling of the selvatic YFV-1D on Brazilian Ae. albopictus mosquitoes, (ii) evaluate their potential to be transmitted to a vertebrate host, and (iii) deepen the transmission of the experimentally selected viruses by field-collected mosquito populations.

Aedes albopictus is an important vector for transmitting arboviruses, such as Dengue, Chikungunya, West Nile or Zika viruses. Its worldwide distribution due to its high ability to adapt to variable environments makes this species a serious threat. This mosquito also better transmits Chikungunya than Dengue virus, and many studies are still trying to understand the deep relationships between these viruses and their vectors in order to develop new control strategies. Moreover, it is now well known that retroviruses partially integrate into host's genomes since it is mandatory for their replication cycle. Interestingly, Retroviridae are not the only viral family capable of host integration. Indeed, in the last decade, owing to new molecular technologies such as next-generation sequencing and bioinformatic tools, non-retroviral integrated RNA virus sequences (NIRVS) have been found into many animal genomes, including Aedes mosquitoes. This came as a surprise since RNA viruses do not have DNA intermediate in their replication cycle. However, little is known about these integrations and many questions remained unsolved. The aim of this project is to assess the production of NIRVS in persistently-infected cells from Ae. albopictus and Ae. aegypti. It is divided in several critical points : the first one is to know how fast the virus can integrate into the cell genome. The second one is to determine which part of the viral genome can integrate and finally, where can it integrate in the genome. This will allow us to understand the virus/host interaction and if NIRVS formation is a mechanism that vectors/hosts evolved as a general response to RNA viruses.

As a result of combined climate change and globalization (increased flow of travelers and goods), the distribution of the mosquito Aedes albopictus is expanding significantly outside tropical regions. Ae. albopictus has already established stable colonies in 20 European countries (https://ecdc.europa.eu/en/publications-data/aedes-albopictus-current-known-distribution-june-2018). Being the main mosquito that can be incriminated in the transmission of chikungunya, dengue, and zika viruses in Europe, Ae. albopictus were responsible for the first autochthonous cases in France and Italy. Accordingly, the European countries that are infested with Ae. albopictus are under the risk of arboviral diseases outbreak. The vector competence analysis of European Ae. albopictus is pivotal for evaluating the potential risk of diseases transmission. In this study, we analyzed the viral susceptibility of several European Ae. albopictus populations from Croatia, Greece, Montenegro, Italy, Switzerland, and also China (as a control), for chikungunya, dengue, and zika viruses. The results indicated that the European Ae. albopictus were able to transmit chikungunya and dengue viruses whereas they were not an efficient vector for zika virus.

Before the WHO considered it as a public health emergency of international concern in February 2016, Zika virus (ZIKV, Flavivirus, Flaviviridae) was a neglected mosquito-borne virus. First identified in Uganda in a sylvatic cycle, ZIKV has caused in few months millions cases, emerging in the five continents (Latin America, the Caribbean, Southeast Asia/Pacific Ocean, Africa/Indian Ocean, European countries (Portugal, Spain, France, Switzerland, the Netherlands)). We have initiated the most comprehensive study on vector competence with almost 50 mosquito populations belonging to five main species (Aedes aegypti, Aedes albopictus, Aedes japonicus, Culex pipiens, Culex quinquefasciatus) infected with 3 different ZIKV and examined at 3 days post-infection (7, 14, and 21). The objective of the project will be to run a meta analysis on vector competence and to assess to which extent each mosquito species contributes to ZIKV transmission according to the geographical location and the viral genotype. It will help to improve our understanding of the vector status and adapt surveillance, prevention, and control of Zika.