What term describes a newly discovered virus that has just started spreading to new populations?

The term that describes a newly discovered virus that has just started spreading to new populations is "emerging virus." Emerging viruses are typically those that have recently appeared in a population or have been identified for the first time. They can be new viruses or existing viruses that have mutated, allowing them to infect new hosts or spread in new areas.

Emerging viruses can have significant public health implications, especially when they lead to outbreaks or epidemics, as seen in certain zoonotic diseases that jump from animals to humans. The classification of a virus as "emerging" highlights its novel characteristics and the need for close monitoring, research, and response strategies to manage potential risks to human health.

Understanding the concept of emerging viruses is crucial in epidemiology and public health as they often require distinct approaches for prevention and control compared to established pathogens, which may already be well understood.