What causes emergence or re-emergence of infectious diseases?
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
