The disease is spreading dramatically, in line with rapid urbanisation around the world, because one of its key mosquito vectors lives mainly in urban areas.

Dengue fever is a severe, flu-like illness that affects tens of millions of people every year but seldom causes death. Dengue haemorrhagic fever, a more dangerous variant, can kill more than 20 percent of its victims if left untreated.

There are no cures, but treatment of symptoms such as dehydration saves many lives. Experts are cautiously optimistic that an effective treatment will be found in a few years time.