© REUTERS/Sukree SukplangBats appear to be the source of the coronavirus, but it's not yet clear which type, or types, of animals were the "intermediate hosts" that passed the virus on to humans.

• SARS-CoV-2 is just one of many coronaviruses, and most of them jump from animals to humans.
• Bats are especially notorious for hosting a number of harmful viruses in the past including SARS, MERS, and Ebola.
• It's unclear where the novel coronavirus comes from but researchers have considered bats and pangolins as a possible source.
• Most humans have already been infected with some strain of coronavirus, experts say, but it's unlikely the illness was as severe as certain cases of COVID-19.

With the world focused on the novel coronavirus, SARS-CoV-2, spreading around the world and claiming tens of thousands of lives as of this writing, it's easy to forget that it's part of a broader collection of coronaviruses. And those coronaviruses have been infecting humans for decades.

"Coronaviruses are a group of viruses that cause a wide range of illnesses, most of which lead to upper respiratory infections," said Jacqueline Vernarelli, PhD, Sacred Heart University director of research education and an assistant professor of public health.

Her colleague, Sofia Pendley, PhD, Sacred Heart University's clinical assistant professor of public health, said that humans first discovered coronaviruses in the 1960s, and learned the virus class can infect both humans and animals, meaning it's what experts call zoonotic.

There's a common theory yet to be proven that the COVID-19 virus originated in bats and then mutated, where it could jump to humans and survive. After all, "bats have been the source of other high-profile zoonotic viruses," Pendley said. Viruses like SARS, MERS, and Ebola.

Pendley, however, cautioned that while this theory is certainly possible, it's also possible upon further inspection that SARS-CoV-2 could have come from a different animal. For example, researchers have found a coronavirus very similar to SARS-CoV-2 in pangolins. But, again, it's unclear who animal patient zero is for COVID-19.

Both Pendley and Vernarelli said the novel coronavirus is one of many viruses to mutate and jump from animals to humans. They called the phenomenon a "spillover event." And it's extremely common.