Emerging infectious disease is the one which has recently started to spread in human population. Either its cases are going up or its geographic range is expanding. Ex: HIV AIDS and H1N1 virus. Reemerging infectious disease is the one which had declined substantially in the past but now is emerging again. It survived in the past and adapted to the new environment to reemerge. Ex. Dengue and West Nile virus
Since 1970s around 40 infectious diseases have been discovered. There are many reasons for the spread of infectious diseases. As humans are able to travel anywhere they are getting exposed to foreign environment a lot. Population is also increasing which has lead to people living very close to each other. Contact with animals has also increased leading to exposure to various new pathogens.
