Viruses are the simplest of all living, gene-bearing life forms, they infect host cells with their genetic material and then reproduce. They are found in humans, plants, bacteria, and other places where they can infect cells, adapt, and change.
Recently, new infectious diseases are foreseen as a major threat to global public health in this century. Most of these are caused by viruses that are able to cross the host species barriers as zoonoses or further establish human-to-human transmission.
Environmental and social changes, frequently the result of human activities, combined with the ongoing evolution of viral and microbial variants, have increased the likelihood that emerging infections will continue to appear and possibly increase, emphasizing the need for effective surveillance.