How the new coronavirus stacks up against SARS and MERS – Science News

Coronaviruses, one of a variety ofviruses that cause colds, have been making people cough and sneeze seeminglyforever. But occasionally, a new version infects people and causes seriousillness and deaths.

That is happening now with the coronavirus that has killed at least 26 people and sickened at least 900 since it emerged in central China in December. The World Health Organization is monitoring the viruss spread to see whether it will turn into a global public health emergency (SN: 1/23/20).

Among the ill are two people in theUnited States who contracted the virus during travels in China. A Chicago womanin her 60s is the second U.S. case of the new coronavirus, the Centers forDisease Control and Prevention confirmed January 24 in a news conference.

Officials are currently monitoring 63people across 22 states for signs of the pneumonia-like disease, includingfever, cough and other respiratory symptoms. Of those people, 11 have testednegative for the virus. Two, including the newest case and anotherpatient in Seattle, tested positive, the CDC reported (SN: 1/21/20).

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France reported two cases on January 24as well, the first in Europe.

Much still remains unknown about the new coronavirus (SN: 1/10/20), which for now is being called 2019 novel coronavirus, or 2019-nCoV. Lessons learned from previous coronavirus outbreaks, including severe acute respiratory syndrome, or SARS, and Middle East respiratory syndrome, or MERS, may help health officials head off some of the more serious consequences from this virus outbreak.

Coronaviruses are round and surroundedby a halo of spiky proteins, giving them a resemblance to a crown or the sunswispy corona.

Four major categories, or genera, ofcoronavirus exist. Theyre known by the Greek letters alpha, beta, delta andgamma. Only alpha and beta coronaviruses are known to infect people. Theseviruses spread through the air, and just four types (known as 229E, NL63, OC43and HKU1) are responsible for about 10 to 30 percent of colds around the world.

What makes a virus a coronavirus is onlyloosely enshrined in its DNA. The coronavirus designation is less about thegenetics and more about the way it appears under a microscope, says Brent C.Satterfield, cofounder and chief scientific officer of Co-Diagnostics, acompany based in Salt Lake City and Gujarat, India, that is developingmolecular tests for diagnosing coronavirus infections.

Coronaviruses genetic makeup iscomposed of RNA, a single-stranded chemical cousin of DNA. Viruses in thefamily often arent very similar on the genetic level, with some types havingmore differences between them than humans have from elephants, Satterfieldsays.

The new viruss proteins are between 70and 99 percent identical to their counterparts in the SARS virus, says KarlaSatchell, a microbiologist and immunologist at Northwestern University FeinbergSchool of Medicine in Chicago.

Usually coronavirus illnesses are fairly mild, affecting just the upper airway. But the new virus, as well as both SARS and MERS, are different.

Those three types of betacoronavirusescan latch onto proteins studding the outside of lung cells, and penetrate muchdeeper into the airway than cold-causing coronaviruses, says Anthony Fauci,director of the U.S. National Institute of Allergy and Infectious Diseases inBethesda, M.D. The 2019 version is a disease that causes more lung diseasethan sniffles, Fauci says.

Damage to the lungs can make the virusesdeadly. In 2003 and 2004, SARS killed nearly 10 percent of the 8,096 people in29 countries who fell ill. A total of 774 people died, according to the WorldHealth Organization.

MERS is even more deadly, claiming about30 percent of people it infects. Unlike SARS, outbreaks of that virus are stillsimmering, Fauci says. Since 2012, MERS has caused 2,494 confirmed cases in 27countries and killed 858 people.

MERS can spread from person to person,and some superspreaders have passed the virus on to many others. Mostfamously, 186 people contracted MERS after one businessman unwittingly broughtthe virus to South Korea in 2015 and spread it to others. Another superspreaderwho caught MERS from that man passedthe virus to 82 people over just two days while being treated in a hospitalemergency room (SN: 7/8/16).

Right now, 2019-nCoV appears to be less virulent, with about a 4 percent mortality rate. But that number is still a moving target as more cases are diagnosed, Fauci says. As of January 23, the new coronavirus had infected more than 581 people, with about a quarter of those becoming seriously ill, according to the WHO. By January 24, the number of reported infections had risen to at least 900.

An analysis of the illness in the first41 patients diagnosed with 2019-nCoV from Wuhan, China suggests that the virusacts similarly to SARS and MERS. Like the other two, 2019-nCoV causespneumonia. But unlike those viruses, the new one rarelyproduces runny noses or intestinal symptoms, researchers report January 24in the Lancet. Most of the peopleaffected in that first group were healthy, with fewer than a third havingchronic medical conditions that could make them more vulnerable to infection.

Coronaviruses are zoonotic, meaning theyoriginate in animals and sometimes leap to humans. The first 2019-nCoV infectionsdetected in December were in patients who had visited the Huanan seafood marketin Wuhan. The market was closed January 1, but health officials have yet todetermine from which type of animal the virus jumped to humans.

Bats are often thought of as a source ofcoronaviruses, but in most cases they dont pass the virus directly on tohumans. SARS probably first jumped from bats into raccoon dogs or palm civetsbefore making the leap to humans. All the pieces necessary to re-create SARSare circulatingamong bats, though that virus has not been seen since 2004 (SN: 11/30/17).

MERS, meanwhile, wentfrom bats to camels before leaping to humans (SN: 2/25/14). A paper published January 22 in the Journal of Medical Virology suggeststhat the new coronavirus has components from bat coronaviruses, but that snakes may havepassed the virus to humans. But many virologists areskeptical that snakes are behind the outbreak (SN: 1/24/20).

It depends on the coronavirus, butneither SARS or MERS have been able to sustain human-to-human transmission theway influenza viruses can, Fauci says. Thats because the viruses havent fullyadapted to infect humans, and maybe they never will, he says.

Still, this is a family of viruses thatwas formerly just the common cold, he says. But now, in the last 18 years,weve had three examples of it jumping species and causing serious disease inhumans. He and colleagues wrote an article publishedJanuary 23 in JAMA to illustrate whatthey see as the growing threat from coronaviruses.

In Wuhan, the new coronavirus has beenable to transmit down a chain of up to four people, health officials said. Fivemembers of a family from Shenzhen, China caught the virus when they visitedinfected relatives in Wuhan, researchers report January 24 in the Lancet. Travelers have also carried thevirus from China to at least seven other countries, including the UnitedStates. No human-to-human transmission has yet been reported outside of China,the WHO said. All of the deaths have also been in that country.

Epidemiologists are franticallycalculating how infectious the new virus is, says Maimuna Majumder, acomputational epidemiologist at Boston Childrens Hospital and Harvard MedicalSchool.

The number that describes how manypeople a newly infected person is likely to pass a virus to is called R0,pronounced Rnaught (SN: 5/28/19). SARS, forinstance, had an R0 between two and five, meaning that in a fullysusceptible population an infected person could potentially spread the virus totwo to five others. (Highly contagious measles, in comparison, has a R0from 12 to 18.)

Estimates for the infectivity of the newvirus range from the WHOs estimate of 1.4 to 2.5 to a much bigger 3.6 to 4.0calculation from Jonathan Read of Lancaster University in England andcolleagues. Reads group estimates that only about5.1 percent of cases in Wuhan have been identified. The researchersreported the preliminary results January 24 at medRxiv.org.

Thats probably not because the Chinesegovernment is covering up how bad the outbreak is, Majumder says. Many peoplemay have had only mild symptoms or none at all. Those people probably wouldntgo to the doctor and get tested for the virus.

Majumder and Harvard colleague KennethMandl used a different method to calculate R0 for the new virus,estimating based on cases reported as of January 22 that its transmissibilityfalls from2.0 to 3.3. Their results were posted to SSRN on January 23.

Meanwhile, Christian Althaus and JulienRiou, both of the University of Bern in Switzerland, posted data to Githubsupporting their calculation that the new viruss infectivity is between 1.4 and 3.8. Each of thosecalculations was arrived at using different methods. While they are slightlydifferent, they overlap, and Majumder says shes reassured that the numbers aresimilar.

Similar infectivity to SARS doesnt meanthe new virus will spread like that one did.

Having SARS in [our] history can helpinform some these decisions that were going to make now. Back then, we wereless prepared than we are now, Majumder says.

For now, all doctors can do is treatsymptoms of the new disease. Researchers have also developed some experimentaltreatments based on SARS and MERS, including antibodies that may help combatthe infections, Fauci says.

Getting samples of the new virus mayallow researchers to develop monoclonal antibodies in the lab. Or scientistsmay be able to take immune B cells from people who already have recovered fromthe virus to produce antibodies to help other infected people.

Some antiviral medications have shown promise in treating MERS, and are being tested for their effectiveness against 2019-nCoV. Experimental vaccines, Facui wrote in JAMA, including some based on RNA, are also in the works.

Erin Garcia de Jesus contributed to reporting of this story.

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How the new coronavirus stacks up against SARS and MERS - Science News