Dengue

Dengue is the most important arboviral disease of humans. Dengue and the related syndromes of dengue haemorrhagic fever and dengue shock syndrome are a leading cause of child mortality in Asia. The incidence and geographical distribution of dengue have increased dramatically since the late 1950s and, in particular, over the last decade. The reasons include the combined effects of several factors: unprecedented population growth and unplanned and uncontrolled urbanization producing a large at-risk population; increased air travel resulting in the rapid spread of dengue viruses to new areas by the movement of infected people; and a lack of effective control of Aedes aegypti mosquitos that have flourished under these conditions (130). Ae. albopictus has been successfully introduced to areas where it was never present before.

Dengue is not now present in Europe, although in the late nineteenth century and up until 1948 it was reported from Crete, Egypt, Greece, Lebanon, Palestine, Syria and Turkey (131). In the past decade, cases have been reported from Djibouti, Saudi Arabia and possibly Yemen. Dengue is included in this report because there is a risk it may be re-introduced into the European Region.

The principal vector of dengue is the mosquito Ae. aegypti, which is adapted to urban environments. Historically, Ae. aegypti has been recorded in several European and North African countries in the Mediterranean region, including France and Portugal. The distribution of Ae. aegypti closely follows the 10 °C winter isotherm (132), and currently includes sub-Saharan Africa and some countries bordering the Persian Gulf.

Another dengue vector, Ae. albopictus, is currently extending its range in Europe. It was introduced into Italy in 1990 and has been reported from 10 regions and 19 provinces since. It has also been separately reported from Albania since 1979. The climatic limits to the distribution of Ae. albopictus are a monthly mean winter temperature below 0 °C, a mean annual rainfall exceeding 50 cm and a mean summer temperature exceeding 20 °C. Countries in the European Region that currently meet such criteria include Albania, France, Greece, Portugal, Spain, Turkey and the Federal Republic of Yugoslavia (133).

Epidemiological studies have shown that temperature is a major factor in dengue transmission in urban areas (9). An increase in global mean temperature of 2 °C by 2100 can potentially increase the latitudinal and altitudinal range of transmission of the disease. In temperate locations, climate change would increase the length of the transmission season (134).

Focks et al. (135) have developed and validated a mathematical model of dengue transmission. The model indicates that dengue transmission could occur in Athens for a short period in late summer under current climate conditions if the vector and virus were introduced (134). This is consistent with observed transmission, as Athens experienced a large outbreak of dengue in 1928. An increase in mean temperature would only result in seasonal dengue transmission in southern Europe if the vector and virus were to be established.

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