State of the art and objectives
Traditional means of controlling arbovirus diseases include vaccination of susceptible vertebrates and mosquito control, but in many cases these have been unavailable or ineffective. The increased disease incidence of arbovirus infections points to the need for new approaches to disease control.
Arboviruses are transmitted by arthropods to vertebrate hosts after amplification and dissemination from the midgut to various other tissues, in particular the salivary glands. It is now clear that arthropod saliva, injected into the host skin during a blood meal plays a crucial role in the vector’s capacity to effectively transfer pathogens during the process. Enhancement of some viral infections (Cache Valley, vesicular stomatitis New Jersey, West Nile) has been associated mosquito saliva, although the molecules involved in this process have not been identified yet. Moreover, most of the studies were performed with laboratory strains (mosquitoes and viruses), which are far from representing the field variability of circulating pathogens and vectors. The discovery of molecules implied in the tuning of the vertebrate immune system during pathogen transmission might constitute the basis to new approaches aiming at blocking the transmission of pathogens by focusing on the vectors.
We therefore propose to analyze the role of the saliva of mosquitoes known to be vectors of Rift Valley fever (RVF) in Senegal in the modulation of the viral transmission to mammals. RVF represents a public health problem in several African countries. Preliminary data obtained from one partner indicate that Aedes aegypti and Aedes vexans saliva indeed modulates RVF transmission and dissemination in a murine model, showing that immunomodulators are present in this saliva. The question that we want to address in our program is whether salivas of the main anthropophilic RVF vectors in Senegal play the same role and if yes whether immunomodulatory molecules can be identified in these species.
A list of RVF potential vectors has already been established in Senegal. We will focus our study on two species in contact with humans: Aedes vexans arabiensis and Culex poicillipes. Anopheles gambiae will be used as control, since it has not yet been demonstrated to transmit RVFV. Human exposure to their saliva will be tested by detecting immune response to salivary components using human sera from exposed individuals from Kedougou collection. Immune reactive salivary proteins will be identified by proteomic approaches (1DE-2DE and MS/MS). Moreover, we will determine whether RVFV will be able to modify the composition of mosquito’s saliva by quantifying the modulation of expression of salivary proteins using proteomic approaches. In parallel, the effect of their saliva on RVF transmission will be tested in mice. Proteomics studies will be carried out to determine which molecules are involved in this effect. Salivary gland extracts will be fractionated in order to highlight the active fractions, the composition of which will be determined by LC-MS/MS. Recombinant proteins will be produced if necessary to refine the experiments. Immunization against the candidate proteins will be performed and effect on RVFV transmission determined.
Expected results and perspectives
We will determine whether the facilitating effect observed with laboratory strains of Aedes aegypti and vexans vexans salivas can be extended to other vectors like Aedes vexans arabiensis, Culex poicillipes and at least identify candidate immunomodulatory proteins. We will determine whether these proteins are naturally immunogenic or not and whether their expression is modulated in presence of the virus in salivary glands. These preliminary data will pave the way to test the feasibility of the preparation of a vaccine directed against the salivary components in the blocking of the transmission of the virus by the vector. Being given the potential of transmission of arboviral diseases by the vectors studied, this approach could be used to block the transmission of other pathogens.