Coronavirus origin: Where did COVID-19 come from?

SAN FRANCISCO -- The novel coronavirus was first discovered in China, and it rapidly spread around the globe. But where did it come from?

"Based on everything that scientists have looked at of the genetic material, of this coronavirus, the similarity is closest to a virus in a bat," said ABC7 News Special Correspondent Dr. Alok Patel, a member of our team of coronavirus experts.

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Scientists believe a bat likely infected another animal before it infected humans. The intermediary animal is still a mystery but some scientists suspect it's likely a scaly mammal called a pangolin.

"Then the virus evolved. It changed form, and it became ready to infect humans at a large scale," said Dr. Patel.

How it got to humans is still unknown.

"Scientists are still trying to figure it out right now, as well as trying to figure out where exactly that animal origin is because understanding this could help us understand the next pandemic," said Dr. Patel.

The novel coronavirus is a zoonotic disease, meaning an infection that can jump between different species.

"Both SARS and MERS are examples of viruses that came from mother nature," said Dr. Patel. "In the case of SARS, scientists believe the virus came from a bat then went to a civet cat, and then infected humans. In the case of MERS, they believe the intermediary animal was a camel."

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Humans have been fighting off zoonotic diseases forever.

"Now the World Health Organization estimates that 60% of all human pathogens have a zoonotic origin," said Dr. Patel. "You might be saying I've never heard of a zoonotic disease, yes you have. Because of rabies, salmonella, West Nile Virus, Ebola, and coronavirus, this one, are all examples of zoonotic diseases."

Some zoonotic diseases cause a mild illness while others can spread quickly, infecting, and potentially causing a lot of death. Sometimes a disease shows up and our immune systems have never seen it before, making it difficult for our bodies to fight it off.

There are many ways for zoonotic diseases to be passed around. Animal to person, person to person, in food, even in water. Even the flu is a zoonotic virus.

"We suspect the 1918 flu was an avian flu," said Dr. Patel.

The 1918 flu pandemic is believed to have killed 50 million people and infected a third of the global population at the time. Though it was called the Spanish Flu, researchers now believe it started in the U.S., on a pig farm in Kansas.

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Here's what some experts believe happened: a bird with the flu and human with a common seasonal flu infected a pig. The two flus mutated in a pig and created a new virus.

"Now the reason the 1918 flu was so deadly, similar to this coronavirus, is because humans had no immunity against it," said Dr. Patel.

That's why understanding where the novel coronavirus came from is key to understanding how we got it. One clue might be in those spiky proteins that allow the virus to infect you. And these specific proteins work dangerously well and have never been seen before.

"This is important, this is why every single major scientific journal and authority believe that the virus came from nature, and not a lab," said Dr. Patel.