Molecular Mechanism of IMD (NF-kB) Inhibition by Dengue Virus in the Mosquito Aedes Aegypti, and Implications for Transmission and Emergence

Dengue virus is the most important mosquito-borne virus causing human disease. Almost half the world's population is at risk of dengue virus infection, mostly in tropical low and middle-income countries. Approximately 400 million people are infected each year, with about 100 million cases of the severe flu-like dengue fever and 500,000 cases of the more severe and potentially fatal dengue haemorrhagic fever. The major impact of dengue disease, on top of significant suffering and loss of life and economic productivity, is that underdeveloped healthcare systems are overwhelmed during the almost annual epidemics experienced by many countries, affecting routine and emergency medical care. There are no medicines to treat dengue and the only licensed vaccine is imperfect and not recommended for widespread global use. Dengue virus is transmitted by mosquitoes and cannot spread directly between humans. When a mosquito feeds on an infected person, it too becomes infected with dengue virus. The virus is passed on when the mosquito feeds on another person, causing that second person to become infected. Preventing transmission through the mosquito is therefore an effective way of reducing the global disease burden. The mosquito that usually transmits dengue virus is the 'yellow fever mosquito' (Latin name Aedes aegypti). Like humans, mosquitoes have an immune system that protects them against viral diseases. The immune response of the yellow fever mosquito springs into action when the insect is infected with viruses, but not all arms of the immune system are able to fight dengue virus. We discovered that this is because dengue virus actively blocks certain parts of the immune response. This grant will investigate how dengue virus escapes from these arms of the immune system, a first for any mosquito-borne virus. Ultimately, this will allow us to develop ways of strengthening the immune system of mosquitoes to stop them from being infected with dengue virus, which will reduce transmission and protect people from dengue disease. Our first goal is to work out how dengue virus blocks mosquito immune responses. Dengue virus makes ten proteins when it infects a mosquito, and we predict that one of these proteins disrupts mosquito immune responses. We will identify which protein can do this, and how. Our second goal will look at this question from a different angle by asking how important certain arms of the mosquito's immune response are for fighting dengue infection. We will do this by looking at what happens to the virus when we grow it in mosquito cells that lack these parts of the immune response. These first two goals will be researched using cells taken from mosquitoes, which are easy to work with in the lab and useful for finding out the fine details of how dengue virus hides from the mosquito immune system. However, we cannot use these cells to study transmission. For this reason, the third and final goal of this grant is to repeat key experiments from the first two goals in yellow fever mosquitoes in the laboratory to check that our results are relevant to what happens in an actual mosquito. There are four different strains of dengue virus, some of which behave very differently from one another, so we will also check whether our results can be extrapolated to all four dengue strains. Together, our experiments will tell us how dengue virus blocks mosquito immune responses, and how important the ability to escape certain mosquito immune responses is for the transmission of dengue virus. In the future, this information will allow us to reduce the global burden of dengue disease by making the yellow fever mosquito's immune response stronger and better able to fight dengue virus in order to prevent disease transmission.