Dengue is a mosquito-borne infection which in recent years has become a major international publichealth concern. Dengue is found in tropical and sub-tropical regions around the world, predominantly inurban and semi-urban areas.
Dengue haemorrhagic fever (DHF), a potentially lethal complication, was first recognized in the 1950s during the dengue epidemics in the Philippines and Thailand, but today DHF affects most Asiancountries and has become a leading cause of hospitalisation and death among children in several ofthem.
There are four distinct, but closely related, viruses that cause dengue. Recovery from infection by oneprovides lifelong immunity against that serotype but confers only partial and transient protectionagainst subsequent infection by the other three. There is good evidence that sequential infectionincreases the risk of more serious disease resulting in DHF.
The global prevalence of dengue has grown dramatically in recent decades. The disease is now endemicin more than 100 countries in Africa, the Americas, the Eastern Mediterranean, South-east Asia and theWestern Pacific. South-east Asia and the Western Pacific are most seriously affected. Before 1970 onlynine countries had experienced DHF epidemics, a number that had increased more than four-fold by1995.
Some 2500 million people -- two fifths of the world's population -- are now at risk from dengue. WHO currently estimates there may be 50 million cases of dengue infection worldwide every year.
In 2001 alone, there were more than 609000 reported cases of dengue in the Americas, of which 15000 cases were DHF. This is greater than double the number of dengue cases which were recorded in thesame region in 1995.Not only is the number of cases increasing as the disease is spreading to new areas, but explosiveoutbreaks are occurring. In 2001, Brazil reported over 390000 cases including more than 670 cases of DHF.
The spread of dengue is attributed to expanding geographic distribution of the four dengue viruses andof their mosquito vectors, the most important of which is the predominantly urban species Aedesaegypti. A rapid rise in urban populations is bringing ever greater numbers of people into contact withthis vector, especially in areas that are favourable for mosquito breeding, e.g. where household waterstorage is common and where solid waste disposal services are inadequate.