Human Coronavirus Types

David Levine

The virus that is currently causing so much fear around the world is commonly called the coronavirus. In fact, public health experts refer to it as the novel coronavirus -- and not because it's a good read. In this case, novel refers to new because the coronavirus disease, or COVID-19, is just the latest version of a virus that has been around probably longer than humans.

A paper titled "A Case for the Ancient Origin of Coronaviruses," in a 2013 edition of the Journal of Virology reports that while the most recent common ancestor of these viruses was known to exist about 10,000 years ago, it's more likely that early versions of the virus have been around for millions of years. And with the number of coronavirus disease cases increasing in the U.S. and worldwide daily, there is growing interest about the origins of this virus and others like it.

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Connection to Animals

Coronaviruses most typically cause disease in animals, specifically birds and mammals like bats and pigs. The authors of the paper that appeared in the Journal of Virology suggest that these animal hosts began diversifying tens of millions of years ago, and the virus probably evolved with them.

Occasionally, the virus mutates so that it can also infect humans. A Feb. 26, 2020, article in Nature reports that the current virus may have spread from bats or pangolins, a scaly anteater that inhabits China. Bats are common coronavirus sources, and the pangolin is a suspect because of a genetic analysis comparing the human virus and one found in the animal. But experts aren't yet certain of the origins of the coronavirus disease.

Wherever it came from, it's far from the first coronavirus to make humans sick. The scientific name of the current virus is SARS-CoV-2 because it is similar to the one that caused the outbreak of SARS, or severe acute respiratory syndrome, from 2002 to 2004. Another virus like this one caused MERS, or Middle East respiratory syndrome, which first appeared in 2012. According to the U.S. Centers for Disease Control and Prevention, all these viruses are known as a betacoronavirus, one of four subgroups of coronavirus, and all most likely originated from a single animal population.

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Known Types of Human Coronavirus

Coronaviruses were first discovered and identified in the mid-1960s, the CDC reports. They are called coronaviruses because the surface of the virus is covered with spiky proteins that give it the appearance of a crown.

There are seven known types of coronavirus that affect humans, says Dr. John Swartzberg, clinical professor emeritus of infectious diseases and vaccinology at the University of California--Berkeley School of Public Health.

All types cause upper respiratory symptoms like sneezing and coughing, and they may also cause fever. Most types of coronavirus are relatively harmless, Swartzberg says. "All but three of them cause the common cold. They cause about one-third of all the colds in children," he says.

These human coronaviruses, which go by the numbers HCoV-229E, HCoV-NL63, HCoV-OC43 and HCoV-HKU1, continually circulate throughout the global human population and cause infections in both adults and children worldwide, according to the CDC.

"But three do more than that: SARS, MERS and now this one," Swartzberg says. When a virus transmits from animal to human, "the vast majority of the time it is dead end for the virus," he says. But on occasion it can multiply and transfer. "That rarely happens, but when it does, it usually causes a severe disease because we have no immunity to this virus," he says.

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Cracking the Genetic Code

At this point , health care experts don't know if exposure to the virus will help the body develop immunity to it. They also aren't certain if this virus will continue to circulate, like MERS, or effectively disappear, like SARS. "We don't know exactly what part of the virus to build a vaccine against," Swartzberg adds. "We have some ideas, but there is a long way to go to build a vaccine."

However, science gets closer every day. On March 2, a research team that included the University of Chicago, the U.S. Department of Energy's Argonne National Laboratory, the Feinberg School of Medicine at Northwestern University and the University of California--Riverside School of Medicine announced they may have found a potential drug target.

They identified a newly mapped protein of SARS-CoV-2 that is 89% identical to the protein from the earlier outbreak of SARS-CoV. Earlier studies showed that inhibiting that protein can slow viral replication, so a drug that does that in this new virus could be effective.

This is just one of about a dozen structures identified, by this team and others around the world, that are now being investigated as possible targets for drugs and vaccines. Andrzej Joachimiak, director of the Structural Biology Center at Argonne National Laboratory's Advanced Photon Source facility and co-director of the Center for Structural Genomics of Infectious Diseases, stresses that his team is working around the clock to decode the genetic mysteries of the virus. "By the end of the year, we may have all the structures identified," he says.

While it may be years before a drug or vaccine is fully vetted and in use, such research is critical not only for this version of the human coronavirus, but also for other new viruses that will inevitably appear in years to come. Continued funding, like that his lab has received from the DOE and the National Institute of Allergy and Infectious Diseases, is important, Joachimiak says, because "viruses are smartly designed molecular machines. They find a way to overcome our defenses."

This is why developing new defenses must be an ongoing battle in the fight against the human coronavirus and other viruses still yet to come.