Presentation of the Unit

Arthropod-borne viruses (arboviruses) are the causative agents of some of the most important emerging infectious diseases, circulating mostly in tropical and subtropical areas and raising threat for developed countries. Among them, some Flaviviruses, Alphaviruses and Bunyaviruses like dengue (DENV), chikungunya (CHIKV) and Rift Valley fever (RVFV) viruses have a large public health impact. Vaccines and antiviral drugs are so far dramatically lacking.

Our efforts focus on the pathogenesis of hemorrhagic fevers associated to RVFV and DENV in mammals and on the molecular basis underlying the lack of pathogenicity in the mosquito vector using RVFV or CHIKV as models. With the aim to extend such studies to another vector borne disease, Lyme disease, our Research unit hosts also the National Reference Center for Borrelia.

Role of nonstructural proteins in pathogenesis

The RVFV nonstructural protein NSs is a factor of virulence antagonizing interferon-ß (IFN-ß) gene transcription. We identified two cellular partners interacting with this protein, p44 of the general transcription factor TFIIH and SAP30 of Sin3A repression complex. Our data show that NSs protein inhibits cellular transcription by two different mechanisms: it prevents assembly of TFIIH through the sequestration of p44 and it maintains the IFN-ß promoter in a repressed state through the formation of repression complexes. To ascertain the role of the interaction of NSs with the cellular partners, RVFV mutants disrupting NSs interaction were produced by reverse genetics and found to be avirulent.

Dengue nonstructural protein NS1 participates to the intracellular stages of viral replication and is associated to the plasma membrane where it modulates the complement system. In addition, it is secreted by infected cells and circulates in the plasma of dengue virus (DENV)-infected patients. We have shown that the NS1 protein represents a hallmark of acute DENV infections and established a diagnostic assay based on NS1 antigen capture in plasma. The kit is commercialized worldwide by Bio-Rad since 2006. Efforts are currently being made to characterize the biological activities of DENV NS1 and define its contribution to viral pathogenesis and the occurrence of hemorrhagic fevers.

Arthropod vector competence

Ae. Albopictus was the vector of CHIKV during the CHIKV outbreak in the Indian Ocean in 2005-2006 whereas there are more than 30 mosquito species, including Aedes and Culex mosquitoes, as potential vector of RVFV. Using an artificial feeding system, we investigated the impact of infection on life history traits and the reproductive success of these mosquitoes. Moreover, ongoing studies are focused on the vertical transmission of mosquitoes, the influence of the endosymbiotic bacterium Wolbachia in virus transmission, the role of RNA interference as a mosquito antiviral defence, and genetic and fitness changes of an arbovirus related to the alternating host replication.

To better characterize the mechanisms implicated in viral transmission, we have developed a differential proteomics-based approach of Aedes aegypti salivary glands non-infected and infected with CHIKV using two-dimensional electrophoresis. Proteins modified in their level of expression or post-translational modifications were identified by MALDI-TOF-MS/MS. These observations will serve as a basis for future work concerning the possible role of these proteins in the interaction between Aedes aegypti, CHIKV and the mammalian host.

Borreliosis, another vector borne disease

In 2008, the National Reference Centre for Borrelia had an active surveillance of Lyme Borreliosis and Ixodes ricinus populations in France (Auvergne, Normandie, Ile de France), Multilocus sequence analysis (MLST) has been used successfully to classify B. burgdorferi s.l. strains isolated both in Europe and the United States.