Dengue fever is a widespread yet poorly understood disease. It has been estimated to infectaround 100 million people a year to a point where it will hinder their day-to- day life, causingfever, headache, vomiting, skin rash and muscle pain. The severity of the disease varieswidely, and though it has a relatively low level of mortality, around 20,000 people per yeardo die as a result of infection. The disease is caused by the dengue virus, of which there arefour distinct varieties, and infection with one type will only confer immunity for that type.The virus is transmitted through bites from mosquitos of the genus Aedes and can thereforespread widely and quickly throughout an area. Once infection has occurred, there are notherapeutic treatments and the best medicine is rest and access to clean potable water.Recently, a few vaccines have been developed against dengue, but whether they are able to effectively prevent dengue remains to be determined. Indeed, the sole commercially available vaccine isonly recommended in areas with very high incidence of the disease. This is because, in thosethat have not been infected with the virus, the vaccine can potentially enhance the severity ofthe disease. This phenomenon is due to antibody-dependent enhancement (ADE). Virusesrely on successfully entering host cells, harnessing the host machinery to replicate and thenreleasing many more copies of the virus out of the cell. As with many infectious diseases,antibodies that recognise the virus are created by the host. These are then sampled bycertain immune cells. This process is a problem in the case of dengue virus. When the rightamount of antibodies remain after an infection (or a vaccination), they cause the virus to betaken into cells that they would normally be unable to enter. It is when these key immunecells get infected that severe disease can occur. Consequently, first infection with disease isusually mild whilst subsequent infection with a different version of the virus can be severe.Working to understand dengue virus and ADE is Professor Eng Eong Ooi of the Duke-NUSMedical School, Singapore. He and his team have made significant progress in increasing theunderstanding of the disease and of the ADE phenomenon. In particular, his work is having adirect impact in the clinic. Ooi explains the aims of his lab: ‘My lab focused on the molecularbasis of antibody-dependent enhancement (ADE) of dengue and other flavivirus infection.We identified the receptors involved in ADE and in inhibiting ADE. Our findings now provideinsights into therapeutic strategies for dengue, as well as how ADE can be exploited toimprove vaccine efficacy”.