Final answer:
An emerging virus is a virus either appearing in a population for the first time or increasing rapidly in incidence or range. SARS-CoV-2 (COVID-19), West Nile virus, and avian influenza H5N1 are examples of emerging viruses with significant implications for global health.
Step-by-step explanation:
An emerging virus is a virus that has appeared in a population for the first time, or may have existed previously but is rapidly increasing in incidence or geographic range. A current example of an emerging virus is the SARS-CoV-2, the virus responsible for the COVID-19 pandemic. Additionally, other examples include the West Nile virus, believed to have been introduced to the United States via an infected air traveler, and the deadly avian influenza strain H5N1, which has a high fatality rate and has caused concern due to its potential to cause a human pandemic.
Zoonotic diseases, which are diseases that primarily infect animals and can be transmitted to humans, make up approximately 75 percent of recently emerging infectious diseases. The H7N9 influenza, which emerged in China in 2013 with a 33% mortality rate, reinforces the ongoing threat of influenza and the need for constant surveillance by organizations like the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC).