Emergent virus

An emergent virus (or emerging virus) is a virus that is either newly appeared, notably increasing in incidence/geographic range or has the potential to increase in the near future.^[1] Emergent viruses are a leading cause of emerging infectious diseases and raise public health challenges globally, given their potential to cause outbreaks of disease which can lead to epidemics and pandemics.^[2] As well as causing disease, emergent viruses can also have severe economic implications.^[3] Recent examples include the SARS-related coronaviruses, which have caused the 2002–2004 outbreak of SARS (SARS-CoV-1) and the 2019–2023 pandemic of COVID-19 (SARS-CoV-2).^[4][5] Other examples include the human immunodeficiency virus, which causes HIV/AIDS; the viruses responsible for Ebola;^[6] the H5N1 influenza virus responsible for avian influenza;^[7] and H1N1/09, which caused the 2009 swine flu pandemic^[8] (an earlier emergent strain of H1N1 caused the 1918 Spanish flu pandemic).^[9] Viral emergence in humans is often a consequence of zoonosis, which involves a cross-species jump of a viral disease into humans from other animals. As zoonotic viruses exist in animal reservoirs, they are much more difficult to eradicate and can therefore establish persistent infections in human populations.^[10]

Emergent viruses should not be confused with re-emerging viruses or newly detected viruses. A re-emerging virus is generally considered to be a previously appeared virus that is experiencing a resurgence,^[1][11] for example measles.^[12] A newly detected virus is a previously unrecognized virus that had been circulating in the species as endemic or epidemic infections.^[13] Newly detected viruses may have escaped classification because they left no distinctive clues and/or could not be isolated or propagated in cell culture.^[14] Examples include human rhinovirus (a leading cause of common colds which was first identified in 1956),^[15] hepatitis C (eventually identified in 1989),^[16] and human metapneumovirus (first described in 2001, but thought to have been circulating since the 19th century).^[17] As the detection of such viruses is technology driven, the number reported is likely to expand.