Update on the global spread of dengue.

The global spread of dengue fever within and beyond the usual tropical boundaries threatens a large percentage of the world's population, as human and environmental conditions for persistence and even spread are present in all continents. The disease causes great human suffering, a sizable mortality from dengue haemorrhagic fever and its complications, and major costs. This situation has worsened in the recent past and may continue to do so in the future. Efforts to decrease transmission by vector control have failed, and no effective antiviral treatment is available or foreseeable on the immediate horizon. A safe and effective vaccine protective against all serotypes of dengue viruses is sorely needed.