Coronavirus: the mystery of the “silent peddlers” without symptoms

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As the coronavirus pandemic swept the world, scientists became increasingly aware of its strange and dangerous behavior. While coughing was observed in many patients, the sense of taste and smell disappeared, and the temperature rose, in others infected the disease did not manifest itself, and they did not realize that they became carriers of Covid-19.

Researchers say it is necessary to understand how many people get sick without symptoms, and whether such “silent distributors” really feed the pandemic.

When flocks gathered in one of the churches in Singapore on January 19, no one could even imagine that this would have global consequences for the spread of the coronaviurs.

On Sunday, one of the sermons was traditionally conducted in Mandarin Chinese. Among the audience was a middle-aged couple who arrived in the morning from China.

The guests looked completely healthy, and no one would have thought that they were carriers of infection. At that time, it was believed that a constant cough should be a mandatory symptom of coronavirus, and that it is in this way that the infection is most likely transmitted.

And there are no symptoms – there is no infection, they thought then.

The Chinese soon left the church, but very quickly things took a sad turn, and no one could understand what was happening. Already on January 22, the woman fell ill, and two days later her husband fell ill. This did not cause any particular surprise, because both of them flew from Wuhan, where the epicenter of the coronavirus arose.

However, next week, three Singaporeans fell ill for no apparent reason – these were the first, most mysterious cases of infection in the country at that time. It was the investigation of the causes of their illness that later led to the discovery of new and very alarming details of how the coronavirus so successfully found new victims.

Mobilization of the “virus hunters”

“We were very puzzled,” says Dr. Vernon Lee, head of the Infectious Diseases Division at the Singapore Ministry of Health. “People who did not know each other managed to recover from the disease without showing any symptoms.”

These new cases did not fit into the picture of what was known about the Covid-19 at that time.

Therefore, Dr. Lee, together with his colleagues and with the help of the police and special “virus hunters”, began an investigation, creating a detailed map of when and where the infected people were. This process is called “contact discovery,” and is now being applied in the UK and in many countries. The process is to identify all those involved in the outbreak of the disease, with the goal of eradicating it. And Singapore has become known for the speed and efficiency of this process.

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At the beginning of the pandemic, Singapore was considered a brilliant example of the fight against the spread of coronavirus

In just a few days, the participants in the investigation were able to interview 191 parishioners of the same church and find out that 142 of them were on duty on Sunday. It quickly became clear that two sick Singaporeans were present at the service along with a Chinese couple.

“They could talk to each other, shake hands during that service,” says Dr. Lee.

This was an important step in the investigation, which could explain how the infection was transmitted, but one key factor was missing. There was no answer to the important question: how could the Chinese transmit the virus, if at that time they did not have any symptoms of the disease.

There was also a much more complicated mystery. The fact of the infection of yet another Singaporean woman, who, however, was not present at that church service, was confirmed. True, she was in the church that day, only a little later. So how could she pick up the virus?

Evidence that no one expected to discover

In search of evidence, the investigators decided to study the recordings of surveillance cameras made that Sunday. And then they discovered something completely unexpected. It turned out that the infected woman, who had visited the church after the Chinese had left, was sitting in the same chair that one of the spouses occupied several hours earlier.

As it turned out, although the husband and wife did not show any symptoms of the disease and felt normal, they were still carriers of the virus. Perhaps the virus passed onto the chairs from their fingers or stood out when breathing, it is not known for sure, but the consequences were the most serious.

When Dr. Lee collated all the evidence, he had only one explanation: the virus was transmitted by people who were infected, but did not realize it. This discovery was significant for the whole world, because so far all recommendations for coronavirus have been limited to recognizing symptoms in oneself and others.

But if the virus spreads without symptoms, quietly and imperceptibly, then how can this disease be stopped at all? Lee recalls how the insight descended on him: “Every time you make a scientific discovery, you want to exclaim“ Eureka! ”You understand that due to the hard work of individuals and entire collectives, you have learned something very important.”

Pre-Symptomatic Infection

And the discovery was what is called “pre-symptom transmission” when a person does not yet know what is already a vector of infection, because he has not yet developed cough, fever and other classic symptoms.

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When the virus seemed to take control in Singapore, the number of infected people began to rise again.

A new study showed that one or two days before the onset of obvious signs of the disease, people can already be infectious, perhaps this is even the most infectious period.

This is potentially a very important factor, because as soon as you realize that you can be sick, everyone who was in close contact with you can be warned about the need for self-isolation.

That is, such isolation can be provided during the key phase of infection, when the symptoms have not yet manifested. However, the question of how the disease can spread without coughing, in which viruses enter the air, remains open.

One version is that infection can occur when talking and just breathing. If the virus is reproduced in the upper respiratory tract, it is possible that part of the virus is excreted with each exhalation. And everyone who is nearby, especially indoors, can easily become infected.

Another potential transmission opportunity is through touch. The virus may fall into your hands when you touch an infected person or a doorknob — or while sitting in a church. Whatever the route of infection, the virus exploits the fact that people lose their vigilance when they are unaware of the possibility of catching the infection.

Some people have no symptoms at all.

This is an even more mysterious scenario, and for the time being scientists simply have no answers. After all, it is one thing to know that people can be contagious even before they have symptoms, and quite another when people become infected, but the symptoms do not appear.

Such an infection is called asymptomatic, since a person is a carrier of infection, but does not get sick. One of the most striking historical examples is the Irish cook, who worked in New York at the beginning of the last century.

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In all the houses where Mary Mallon was hired as a cook, people became ill with typhus, and at least three people died from the disease. At the same time, Mary herself remained completely healthy.

In the end, the connection between the disease and the cook was established, she was the carrier of the infection, although she herself remained healthy. The press christened her “typhoid Mary”, and the authorities sent the woman under lock and key, where she sat for 23 years until her death in 1938.

You cannot be sure of anything

23-year-old nurse Amelia Powell was shocked when she found out that she was an asymptomatic carrier of the infection. At that moment, when the doctor called her and reported the results of the tests, she was just working in the ward of the Cambridge clinic Addenbrook.

Amelia felt normal and believed that she was completely safe, because when working with patients with Covid-19, she used personal protective equipment. However, all her confidence instantly evaporated when, to her horror, the tests gave a positive result.

“The feeling was like they told me about the death of a loved one, it was something unrealistic. I thought that this could not be, just not with me, because I’m in perfect order,” recalls Amelia.

She had to leave work immediately and isolate herself at home.

“Of course, I was worried, because I saw the inside out, so to speak, saw how quickly the condition of patients with coronavirus worsened, and thought what would happen to me.” However, to her great surprise, she never became ill. “Nothing literally happened to me: at home I continued to do exercises, ate normally, slept normally,” Amelia says.

No one knows how many such cases of covert infection exist in the world.

Amelia found out that she had a coronavirus, only because the entire hospital medical staff was required to undergo an examination. The result of this test surprised experts: of more than a thousand people, up to 3% showed a positive result, without showing any symptoms.

Even more asymptomatic people found themselves on the Diamond Princess cruise ship, which the epidemic found off the coast of Japan. The liner was dubbed the “Petri dish”, that is, a real hotbed of infection, because on board there were about 700 cases of infection.

At the same time, three quarters of the identified infected showed no symptoms.

And in one of the nursing homes in Washington, more than half of the inhabitants tested positive for coronavirus, but showed no signs of illness.

There is simply no reliable data

Different studies give completely different data on the number of asymptomatic infections, ranging from 5% to 80%. This was the conclusion of the professor at Oxford University, Karl Henegan, who, together with his colleagues, studied the results of 21 research projects on this topic.

General conclusion? According to scientists, no study can provide reliable data on the number of asymptomatic infected. Moreover, if the tests for Covid-19 will be taken only from people who show symptoms of the disease, and this is what practice in the UK requires, then some cases will be overlooked, possibly many cases, experts add.

The danger of “silent peddlers”

One of the main concerns of the nurse Amelia was that she could, without knowing it, infect one of her colleagues or patients she was caring for with the virus.

“I don’t think it happened because the analyzes of all my colleagues gave a negative result, but it’s still unpleasant to feel that I have been infected for so long,” Amelia says. “And we still don’t know if the asymptomatic is contagious media. It’s very strange, but so far we have a minimum of information on this subject. ”

An alarming signal to the authorities was the results of a study in China, according to which the number of asymptomatic infected people is actually even higher than the number of patients with symptoms.

“Being” silent peddlers “, asymptomatic carriers require increased attention in the interest of containing and controlling the disease,” the scientists write.

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A group of experts who studied the situation aboard the Diamond Princess liner suggested that asymptomatic people are less contagious than people with symptoms, but they could still be an important source of infection.

“Dark matter” of asymptomatic infection

In an attempt to find answers, scientists led by Professor Neil Hall suggest making coronavirus tests for the entire population of Norwich.

“Asymptomatic cases may be the very” dark matter “of the current epidemic,” said Professor Hall. We are talking about the notorious invisible substance, of which, presumably, for the most part the matter of our universe consists, but which has not yet been discovered.

Professor Hall fears that asymptomatic cases, despite all the authorities’ efforts to protect public health, continue to fuel the current epidemic.

“If there are people who do not suspect that they are ill, and at the same time use public transport and medical facilities, this will inevitably lead to an increase in infections,” the scientist says. “Any action in relation to people who come to treatment facilities with symptoms of the disease will only be a half solution to the problem. ”

According to a group of scientists from California, asymptomatic carriers are the “Achilles heel” of our fight against the coronavirus pandemic.

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China is the first to introduce coronavirus bulk testing

They are convinced that the only way to stop the spread of the disease is to identify all infected people by testing, regardless of whether they have symptoms of the disease.

And they propose to pay special attention to health and social welfare workers who are in contact with a risk group.

A similar approach, only on a larger scale, has already been adopted in Wuhan, which, apparently, has become the first focus of the epidemic.

Over 9 days, 6.5 million residents were tested there to identify all carriers, including hidden ones.

Cancel hard quarantine

As quarantine measures become weaker and more people start using public transport, going to work and shopping, the danger of invisible risks increases significantly. At the moment, it is simply impossible to say exactly who in the growing crowd of people can be an involuntary peddler of infection.

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More and more countries are introducing mandatory wear masks.

That is why governments around the world are repeating to their citizens how important it is to jointly identify the contacts of all infected and to comply with the rules of self-isolation. They also recall that maintaining social distance remains one of the most reliable and effective remedies. Well, where it is not possible, people should wear masks, even if they are home-made masks.

When the US authorities announced these measures, they referred to the discovery made in the church of Singapore in January. The meaning of the message is that you should think not only about your own protection, but also about protecting others from yourself in case you are sick, but you have no idea about it.

Many health experts fear that wearing masks may distract people from washing their hands or social distance, or even increase the risk of infection if these masks are not handled properly. However, more and more countries, including the UK, are convinced of the effectiveness of the masks.

Of course, wearing a mask alone will not stop the pandemic, but since we still know too little about the asymptomatic transmission of the virus, any attempt to protect yourself from it is worth it.

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