Emerging infectious diseases are infections that are newly recognized in a population or have existed but whose incidence or geographic range are rapidly increasing or threatens to increase in the near future.
Emerging infections can be caused by:
1. previously unrecognized or undetected infectious agents
2. known agents that are spreading to new geographic areas or populations
3. new infections resulting from changes or evolution of existing organisms.
4. Old infections (whose incidence had significantly declined in the past) reemerging because of an increase in antimicrobial resistance or breakdowns in public health measures or changes in the ecologic transformation of a particular area. This class of diseases is known as re-emerging infectious diseases.
According to the 10th International Conference on emerging infectious diseases, emerging infections account for at least 15% of all human infections. Many emerging diseases are zoonotic but may be food-borne, vector-borne, or airborne. Some of the emerging infectious diseases are Ebola, SARS, MERS, Chikungunya, avian flu, swine flu, Zika, and COVID-19 caused by SARS-CoV-2.