What is coronavirus? An explanation of symptoms and severity

Imagine fencing in every Californian.

That’s essentially what China announced on Friday, quarantining 35 million people, nearly the entire population of our state, to stop the spread of a dangerous new virus before it gains a firm foothold around the globe.

Because the virus – a class of coronaviruses provisionally called 2019-nCoV– is brand new to medical science, no one knows how easily or quickly it is transmitted. And there’s no vaccine.

While mysterious, so far its impact pales in comparison to the common flu virus, which has already killed between 8,200 and 20,000 Americans this winter, according to the U.S. Centers for Disease Control.

There have been two cases of infection with the new virus in the U.S. – in Seattle and Chicago – among people who returned on flights from China’s Wuhan area, the center of the outbreak. Air travel from this region has since been suspended.

In the San Francisco Bay Area, with strong links to Asia, health officials are testing travelers with high fever, a cough and other symptoms.

In Alameda County, a number of patients have been recently tested, according to health department spokeswoman Neetu Balram, but there are no confirmed cases.

Santa Clara County would not share details as to whether anyone had been tested, but a spokesperson said in a statement that the county “has not received any reports of novel coronavirus, and at this time, Santa Clara County residents are at low risk for this virus.”

Although the outbreak is a “very serious public health threat, the immediate risk to the U.S. public is low at this time,” said Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases.

Here is what else you need to know.

Q: Is it too late to stop it?

A: With global travel, the world has become much more vulnerable to the spread of new infectious diseases like this one. A person harboring a life-threatening microbe can easily board a jet and be on another continent when symptoms strike. Few places remain truly isolated or untouched.

While travel has been blocked from central China, the virus has already spread to eight nations: Nepal, Vietnam, Singapore, Japan, South Korea, Taiwan, Thailand and the United States.

In China, two deaths have been confirmed outside the center of the outbreak. And if it gets established in massive international cities like Shanghai, Beijing or Hong Kong, it will be almost impossible to contain.

San Francisco International Airport, which touts itself as the country’s “Gateway to the Pacific Rim,” receives more daily, non-stop flights from Hong Kong than any other U.S. airport.

Q: What is it?

A: It is a coronavirus, one of the five families of viruses that are known to cause respiratory illness, including the coronaviruses, the parainfluenza viruses, and the adenoviruses.

It is composed largely of RNA, rather than DNA. It gets its name from the fact that it appears to have a crown that surrounds the viral particle.

Although the family of coronaviruses is large and well-known, this particular virus is one never seen before.

Q: How did it start?

A: It’s the latest of a growing list of emerging diseases, so called because they seem to appear out of nowhere. Some type of wild game is the most likely source. Health officials in China say it originated in a large seafood market in Wuhan, a city in central China, that also sells wild animals as meat.

These so-called zoonotic viruses – which have no respect for species boundaries — are an ongoing concern for the nation’s disease sleuths.

They start when an animal virus that mutates in a way that allows it to infect humans, or with a virus that people encounter for the first time when they move into a new environment.

The coronavirus that caused 2003’s deadly outbreak of SARS, or severe acute respiratory syndrome, is closely related to those found in bats. The same is true of the virus behind the 2018 outbreak of swine acute diarrhea syndrome, or SADS. Bats are also known reservoirs of the Ebola virus, Marburg virus, Nipah virus, and Hendra virus, even though they usually don’t exhibit symptoms.

Q: What are the symptoms?

A: It was detected due to an unusual spike in cases of pneumonia — lung inflammation, accompanied by cough and phlegm.

Since then, doctors have seen a broader set of symptoms, including fever, cough, and shortness of breath.

People with mild symptoms may not be seeking medical care and recover without incident. That makes it hard to know how dangerous or widespread it is.

Q: How does it spread?

A: Like the cold and flu, it spreads through coughing, sneezing or by leaving germs on a surface that is touched by non-infected people who touch their faces.

Q: Is it easily spread? 

A: According to the World Heath Organization, the current estimate of the reproductive rate of the virus — the number of people, on average, that each infected person infects — is between 1.4 and 2.5.

That’s similar to the cold and flu, but not as infectious as the measles virus, which can live for up to two hours in the air after an infected person coughs or sneezes.

Initially, experts hoped it would only be transmitted by animals tied directly to a Chinese market.

But now there are clear examples of person-to-person spread. On Thursday, the WHO reported an instance of four “generations” of spread: an animal infected a person, who infected another person, who then infected another person.

Q: Where’s the vaccine?

A: The National Institutes of Medicine and several private companies are in the process of developing a vaccine, according to Dr. Anthony Fauci, director of the National Institutes of Allergy and Infectious Diseases.

The effort has been accelerated by Chinese researchers, who quickly sequenced and published the virus’s genome.

But it will be several months before completion of animal testing to prove safety so the first phase of human clinical trials can get underway.  It may be more than a year until a vaccine might be available, according to Fauci. Health care workers would be the first recipients, he said.

Q: What’s next?

A: In addition to creating a vaccine, experts will seek to better understand the virus and its illnesses, and study specimens from patients at different stages of their illness.

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