Why does it happen? Several factors contribute to the emergence and re-emergence of infectious diseases, but most can be linked with the increasing number of people living and moving in the world: rapid and intense international travel; overcrowding in cities with poor sanitation; substantially increased international trade in food, mass distribution of food and unhygienic food preparation practices; increased exposure of humans to disease vectors and reservoirs in nature; and alteration of the environment and climatic changes, which have a direct impact on the composition and size of the population of insect vectors and animal reservoirs. Other factors include a deteriorating public health infrastructure, which is unable to cope with the needs of the population.

Travel has always been a vehicle to spread disease across the world. According to data from the World Tourism Organization, over 550 million travellers were counted at national borders in 1995 and over 117 million of them had crossed continents to arrive at the destination. Luckily, the vast majority of infections brought along with travellers are common worldwide, and the disease is more a nuisance to the individual traveller than to society. The traveller can avoid many health risks with vaccines, protective measures against malaria and good personal hygiene.

For more details, see International Travel and Health, issued by WHO each year and accessible from WHO's website at http://www.who.ch/emc/.

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WHO: RESOLUTION AND RESPONSE In 1995, a resolution of the World Health Assembly urged all Member States to strengthen surveillance for infectious diseases in order to promptly detect re-emerging diseases and identify new infectious diseases. This resolution led to the World Health Organization's establishment of the Division of Emerging and other Communicable Diseases Surveillance and Control (EMC), whose mission is to strengthen national and international capacity in the surveillance and control of communicable diseases, including those that represent new, emerging and re-emerging public health problems.