This article, written by Narveen Jandu , University of Waterloo , originally appeared on The Conversation and has been republished here with permission: Viruses are naturally occurring entities. Viruses have existed on Earth long before humans and vastly outnumber humans. There are more viruses on Earth than there are stars in the universe or cells in the human body.
As a cellular microbiologist who has studied the origin and development of infectious diseases and their prevention, understanding where infectious agents come from is as important, if not more important, to understanding how to combat the rampant spread of diseases within the human population.
Fortunately, only a small fraction — about 200 — of this vast array of viruses can infect humans. Some of the better-known human viral infections include measles, varicella, polio, human papilloma virus, influenza and rhinoviruses, which are typically responsible for the common cold.
An even smaller number of viruses are responsible for the deadliest human infections that we have experienced. In recent decades these include rabies virus, human immunodeficiency virus (HIV), Ebola virus and now, infamously, coronaviruses.
Viruses that circulate in other animals can enter a human population when a variety of human activities allow for consistent and regular interaction with naturally occurring reservoirs. These events involve repeated and routine interaction of humans with these animal hosts.
Some of these interactions take place through the following human activities: hunting, butchering and farming (husbandry), as well as the global trade of animals and domestication of exotic animals as pets. Population growth, global travel and climate change that cause the disruption of habitats further provide opportunities for cross-species transfer.
Cross-species transfer Many of […]