Jonathan Gershoni is professor of molecular cell biology and biotechnology at the Tel Aviv University life sciences faculty. He has researched viruses whose genome is made out of RNA for decades. Without providing a detailed explanation of what viruses with RNA genome are, he explains simply that they are distinguishable from viruses with DNA genome, and that other examples of such viruses, in addition to the coronavirus, are type C hepatitis, HIV (AIDS), and Ebola.
Actually, Gershoni corrects me, the virus afflicting us should not be referred to as coronavirus; coronavirus is a family of viruses, and each member of the family (such as SARS, MERS, and the current virus) has its own name. The current virus, SARS-CoV-2, is the seventh virus in human beings that causes the COVID-19 disease because it first appeared in December 2019. They chose not to call it Wuhan virus (the city of Wuhan in the Chinese province of Hubei, where the disease was first discovered) in order to avoid attributing the epidemic to China. "It is interesting that the 1918 Spanish flu epidemic did not begin in Spain," Gershoni remarks. "The name was taken from the initial reports of the epidemic, which were published in the Spanish press. The Spanish were unhappy about the name attached to the epidemic."
Four other corona family viruses that are infectious for human beings usually cause mild illnesses, such as colds. The SARS and MERS viruses cause severe lung disease. While the current coronavirus is less deadly than its two predecessors, it is far more infectious. "When we classify viruses," Gershoni says, "we look at their genome composition. If we compare the three types of deadly coronaviruses, the current one resembles SARS from 2002 more than MERS. SARS from 2002 was abominable, with a 10% fatality rate. At the same time, there were 'only' 8,000 patients, 800 of whom died."
How do you explain the fact that the original SARS disappeared so suddenly without anything having been done?
Gershoni: "There's really no explanation of why it suddenly disappeared. Isolation was used in the SARS virus, but not on a global scale, as with the current epidemic. There was no vaccine or effective drugs. It disappeared as suddenly as it appeared. The SARS virus spread in 30 countries, while the current coronavirus has already reached over 200 countries. SARS also began in China, moved to Hong Kong, and from there 700 more cases in Taiwan, Canada, and Singapore. There were fewer than 30 in the US, and then there were a few in South Africa, and South Korea. This is a very different profile than the current situation.
"The current virus is a coronavirus and cousin of SARS, but it behaves differently. It causes moderate-to-medium illness in 80% of those affected. Many infected people are completely unaware of it. There are cases in which the symptoms are very mild, and there are cases with no symptoms at all. The problem is that with the new virus, even without any symptoms, those infected can still infect others. The original SARS, on the other hand, infected people only when there were clear symptoms. It was therefore much easier to use isolation, because it was clear who was ill, and whom to keep away from. In contrast, if you have a disease that is very infectious even in the absence of symptoms, it's much harder to act against it.
"Another difference is that this virus is very stubborn. We sometimes see people infected with the disease who appear to have recovered, meaning that they have no symptoms, but the test for the presence of the virus is still positive. Even after patients get well, after their clinical symptoms have disappeared, some of them continue to spread viruses, and can infect other people."
Why is the current virus more infectious than the original SARS?
"Viruses don't infect all of our tissue; they infect only certain cells. Why does a virus infect certain cells and not others? Because there is a cell protein on the target cells that the virus identifies as a receptor, and only cells with receptors can be infected. The virus identifies the receptor on the target cell through the protein in which it is wrapped. The virus's protein envelope accurately identifies the cell receptor suitable for it. Certain viruses therefore infect specific tissues. For example, hepatitis viruses infect liver cells, and corona viruses infect the respiratory passages.
"In recent weeks, it was discovered that the current virus uses the same receptor to which the original SARS virus connects. The receptor is on a lung cell called Angiotensin converting enzyme 2 (ACE2). If the link (between the virus and the receptor) is weak, the virus does not infect effectively. The current virus links itself to the receptor more strongly than the original SARS virus, and so it's more efficient."
Is there a connection between the deadliness of the virus and its ability to spread?
"Disappearance of viruses sometimes results from an especially high mortality rate. If we take a virus that kills 40% of those infected, a situation emerges in which the virus has trouble finding more people to infect, and then it fades away. This is what we saw with the outbreak of Ebola. The disease appeared in a remote area in African forests. After the virus killed people in the village, people kept their distance, and the virus found no one else to infect, so it faded away.
"Another way of preventing a virus is through vaccines. If the prevalence of vaccination in a population reaches 95% or more, 'herd vaccination' is created, in which even people who have not been vaccinated are protected. The problem is created when the extent of vaccination falls below 85% of the population. Then a disease spreads that could have been prevented by vaccination."
What do you think about herd immunity as a way of dealing with the current epidemic?>/i>
"There's a problem. The idea is to isolate older people, with the idea that younger people will get infected, but will get well. There will be cases that don't conform to the statistical pattern, and we'll also see fatalities in the 20-40 age bracket. In the absence of a drug or vaccine, the only thing left to do is social distancing. We have no other tool. Obviously, we should also put a maximum effort into finding a vaccine and drugs."
What you are saying is that the current virus, SARS CoV2, which is very similar genetically to the original SARS virus, behaves differently. We have two viruses, "cousins," in the same sub-group. They are very close genetically, and the original virus faded and disappeared. Can we expect the new virus to also disappear?
"We have no precise explanation of why the first SARS disappeared, and we can't conclude that what happened then will repeat itself by this virus disappearing. At the same time, there are still many unclear things, because we learned about this virus only three months ago."
What do you say about the comparison between the current virus and influenza?
"With flu, we have 500 million people infected, and 500,000 of them die every year. But we have a vaccine for flu, and we have drugs - we have tools for dealing with it. With the current virus, we don't have enough understanding, and we lack means of protection. We have no vaccine or drug, and this doesn't make things easy. We're now in a situation in which over 660,000 people have been infected in two and a half months, and 30,000 people have died. This isn't the behavior of flu, in which the mortality rate is 0.1%.
"The situation now is that the numbers that we're using depend on tests, so that as more tests are conducted, we'll unfailingly discover more patients. As of now, we're in a threatening process of great uncertainty. It would be great if we could continue our lives undisturbed and move the economy ahead without any threat. But we face a difficult decision: what do we save - the health system and public health, or the economy? Unfortunately, I have no solution - as of now, we're unable to guarantee that a purely economic attitude will save the country. In a day or two, we could suddenly see the rate of infection rising geometrically and catastrophically, but then it will be too late, and we won't be able to deal with the disease when it involves widespread mortality. Meanwhile, we should maintain isolation and flatten the infection curve."
Researchers agree: The coronavirus will probably not disappear
Prof. Manfred Green, head of the international master of public health program at the University of Haifa, says that although SARS was far deadlier than the current virus - it caused a severe disease with a high mortality rate - the problem now is much more difficult. "The more deadly a disease," he says, "the easier it is to identify the patients and isolate them from healthy people relatively quickly, and then the virus has nowhere to go."
Why do you think that SARS disappeared so suddenly?
Green: "It's a mystery sometimes why a virus disappears, but it happens, although it's not common. In 1957, we had an H2N2 flu pandemic, and the virus disappeared after a short time. Why? We don't know. Probably, the virus, which came from birds, didn't adapt enough to human beings."
Dr. Ella Sklan, who researches molecular virology in the Department of Clinical Immunology and Microbiology at the Tel Aviv University Sackler Faculty of Medicine, says that the question of whether the current virus will suddenly disappear or stay with us for a long time is the "million-dollar question." "Right now," she says, "we don't know how the virus will behave, whether it will return every year, or disappear. As of now, most of the experts assume that it won't disappear, because it has already spread very widely. All of this, however, is theoretical, based on the behavior of earlier viruses, and it's very difficult to predict how a virus to which the population has no immunity will behave. All we can do right now is try to limit the infection as much as possible in order to avoid overloading the health system."
Dr. Tomer Hertz of the department of microbiology and immunology at Ben Gurion University of the Negev, and a member of the National Institute for Biotechnology in the Negev, believes that the current virus will be with us for quite some time. "At the moment, I see no way that it's going to disappear," Hertz says. "To tell you the truth, there's a reasonable likelihood that it will become one of the seasonal coronaviruses going around the world each year."
Hertz says that with the current virus, "It appears that we passed the self-limiting stage of the virus a while ago. What's important right now is to influence the effective reproductive number of the virus, and this is linked to our behavior. If we following the rules of social distancing, fewer people will get infected, and if we succeed in reaching a stage in which we have mass tests, we'll be in a better situation, because we'll be able to isolate all of the asymptomatic infected people, who now we know exist, and who contribute to the spread of the virus. This is the only way possible to improve our situation in the public and functional space - following the rules and tests. It's not that people will be infected less if we stay at home but the rate of infection will be much slower."
According to Hertz, the mortality rate from the current virus will be 0.5-1% of those infected, far lower than from SARS, whose mortality rate was almost 10%, assuming that the health system functions and does not collapse. "In Italy, for example," Hertz says, "The mortality rate is high, because the health system simply collapsed, and it was impossible to treat all of the patients. Had it been possible to treat all of the patients the mortality rate there would have been significantly lower. Many people believe that the same thing will happen in the UK now, because Boris Johnson understood the situation too late."
Published by Globes, Israel business news - en.globes.co.il - on March 29, 2020
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