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How Did the Novel Coronavirus (COVID-19) Jump the Species Barrier?

Medically reviewed by Susan Kerrigan, MD and Marianne Madsen

The novel coronavirus (COVID-19) pandemic has us all asking questions. Where exactly did it originate? How did it get from China to the West? How serious is it? Am I at risk? 


Most know by now that COVID-19 came from somewhere in China. The current hypothesis is that the virus started in late 2019, originating from bats being sold in the Huanan Seafood Wet Market in Wuhan, China. For the uninitiated, “wet markets” are places where people buy and sell animals, many of which are killed on the spot, sold, and eaten a few hours later by customers. These markets usually sell a variety of exotic animals in addition to the standard chicken and fish. Porcupines, bats, foxes, salamanders, and crocodiles are only the tip of the iceberg. 

Many are wondering how COVID-19 was transmitted from bats to humans. Scientists think that before it made its way to humans, COVID-19 was originally a bat-specific virus called SARS-CoV-2, classified as a zoonosis. Zoonoses are diseases that can jump from animals to people. A study done in March of this year attempted to pinpoint the exact origin of COVID-19 and how exactly it made its way from bats to humans. 

Kristian Andersen, PhD, associate professor of immunology and microbiology at Scripps Research Institute, led the study. He and his team say the virus originated from one of two possible scenarios. 


In the first scenario, the virus evolved through natural selection in an animal host to the point where it became a pathogen, meaning that it could cause disease in hosts that were infected. Then, it jumped to humans. The researchers agree that the most likely host of the virus was bats. However, they think the infected bats passed the virus to another host (currently unknown) which transmitted it to humans. Since in this scenario, the virus would have already been a pathogen before it made its way to humans, it would have spread very quickly and infected people at a high rate.

In the second scenario, researchers propose that a non-pathogenic version of the virus (not yet capable of causing disease) made its way from an animal host to humans, and once within the human population, it evolved into a pathogen. They considered that since viruses similar to SARS-CoV-2 have been found in pangolins (scaly anteaters) pangolins could have transmitted the virus to humans. After the virus spent some time inside the human body, it likely evolved rapidly and spread quickly to others, as in the first scenario.

The problem? Researchers admit that both scenarios are equally likely to have happened. However, if the virus did originate as a pathogen in animals, the likelihood of future outbreaks is much higher, as the virus in a pathogenic state could still be present among animal populations. Chances are lower of the virus being transmitted from animals if it only evolved into a pathogenic state once inside humans.


Whatever the case, it’s important to take COVID-19 seriously and adopt the necessary measures to prevent you or your loved ones from getting the virus.

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