WHO Report on Global Surveillance of Epidemic-prone Infectious Diseases - Dengue and dengue haemorrhagic fever
Beginning with the latter part of the eighteenth century, and throughout the nineteenth and early twentieth centuries major epidemics of dengue-like illness have been reported in the Americas, southern Europe, north Africa, the eastern Mediterranean, Asia, and Australia, as well as on islands in the Indian Ocean, the south and central Pacific and the Caribbean (1). The beginning of these more frequent reports coincides with the time that the Ae. aegypti mosquito, the primary dengue vector, began spreading from Africa throughout the tropics, via sailing vessels used in commerce and in the slave trade, and when people began moving more frequently between continents. The mosquito adapted very well to urban environments, living in close proximity to people, breeding in small containers that collect rainwater and in water storage vessels.
There are a number of ecological factors associated with the middle and later parts of the twentieth century which have lead to a dramatic increase in DF, and to the emergence of DHF as a significant public health problem in the Americas and Asia. First, there has been a large increase in unplanned urbanization, resulting in large populations living in high-density areas with inadequate systems of water and solid waste management. These areas provide excellent breeding places for Ae. aegypti mosquitos.
In addition, two specific occurrences, one in Southeast Asia and the other in the Americas, were additional catalysts for the spread of dengue. First, activities associated with World War II and the immediate post-war period are particularly implicated in the increase of DF and DHF in South-East Asia. The existing water supply and sewage systems were destroyed during the war resulting in more favourable breeding places for Ae. aegypti. Second, the movement of (mostly susceptible) troops to the war theatre for short periods of time, presented the virus with a large supply of new susceptible hosts on a continuous basis, increasing the spread of disease. The subsequent movement of those hosts and or war machinery to other areas facilitated the circulation of virus serotypes throughout the region, and fostered hyperendemicity (the circulation of more than one serotype at the same time). During the post- war period millions of susceptible people from the poor rural countryside moved to the cities, providing a continuous influx of large susceptible populations living in poor peri-urban areas that were hyperendemic for dengue.
This led to both the increase in DF and the emergence of DHF as major public health problems. DHF was discovered in Manila in 1953. There had been sporadic reports of disease with symptoms similar to DHF previously, but these were considered to be unusual occurrences. Since 1953, DHF has been increasing in its frequency, geographical scope, and number of cases.
In the Americas, the lapse in mosquito eradication programmes had important consequence for dengue. The Ae. aegypti eradication programmes to fight against yellow fever were discontinued in the early 1970s. Subsequently, there was a re-infestation of the Americas with Ae. aegypti. The combination of the re-infestation of the Americas with the primary vector for dengue combined with unplanned rapid urbanization and increased travel and commerce has played an important part in the increase of dengue and emergence of DHF in the Americas.