[Global threats from emerging viral diseases].

Emerging viral diseases are nothing new. Smallpox probably reached Europe from Asia in the 5th century, and yellow fever emerged in the Americas during the 16th century as a consequence of the African slave trade. Dengue fever arose simultaneously in South-East Asia, Africa, and North America during the 18th century. In 1918-1919 the so-called Spanish flu spread like wildfire through all five continents, killing between 25 and 40 million people. The second half of the 20th century saw the emergence of HIV/AIDS (1981), among other viral diseases. Even more worrying is the fact that emerging and re-emerging viral diseases have had a tendency to spread more quickly and more widely during the last decade, invading whole countries and continents; witness the recent outbreaks of Nipah virus, West Nile, Rift Valley fever, SARS, monkeypox, avian flu (H5N1) and Chikungunya. The complex factors underlying these new trends are briefly discussed.