Corona virus: the mystery of the carriers and spreaders of the virus without showing symptoms of infection

As the seasons of the Corona virus pandemic unfold, scientists are discovering more evidence about a strange and troubling feature of the virus. While most of those infected with the virus suffer from coughing, fever, and loss of the sense of taste and smell, there are others who do not show any of these symptoms at all and do not know that they are spreading Covid-19 disease, which is caused by the virus.

The researchers say it is important to know who has the virus and is not showing any symptoms and whether they are the "silent spreaders" of the infection.

When a number of worshipers gathered in a church in Singapore on January 19 of this year, none of them realized that this prayer would have global consequences around the spread of the virus.

It was a Sunday and, as usual, a prayer was held in Mandarin, which is spoken by most Chinese. Among the attendees at the Life and Dispatch Church on the ground floor of an office building were a married couple, both 56 years old, who had arrived that morning from China.

When they took their seats they seemed to be perfectly healthy so there was no reason to believe they might be carriers of the virus. At the time, persistent coughing was thought to be the most prominent feature of COVID-19 and was seen as the most likely means of spreading infection and thus the absence of symptoms meant that the virus was unlikely to spread.

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The couple left as soon as the prayer was over. But shortly after that, the situation developed in a way that is not fully understood. The Chinese wife fell ill on January 22 last, and her husband followed her two days later. Because they flew in from Wuhan, the epicenter of the outbreak, this was not too surprising.

But over the next week, three Singaporeans also fell ill for no apparent reason, leading to one of Singapore's first and most surprising cases of the virus. Knowing what happened will lead to the discovery of something new and troubling about how the virus can successfully transmit to new victims.

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Mobilizing "disease investigators"

“We were so perplexed that people who don't know each other somehow make each other sick,” says Dr. Vernon Lee, head of the Department of Communicable Diseases at Singapore's Ministry of Health, without showing any sign of illness. This new batch of cases was not normal in light of what was known about Covid-19 at the time.

So Dr. Lee and his fellow scientists, along with police officers and pathologists, investigated and came up with detailed maps of who, where, and when. This involved what is best known as a contact tracing or contact tracing process, which is similar to a process now being implemented in the UK. This program is seen as an effective system to track down everyone involved in the outbreak and help eradicate it, and Singapore was distinguished by the skill and speed of implementation of this program.

Within a few days investigators spoke to at least 191 church followers and discovered that 142 of them were there on Sunday. They quickly established that two Singaporeans who had contracted the infection were among those present at the prayer service with the Chinese couple.

"They may have talked to each other or greeted each other, as is the norm in such activities in the church," says Dr. Lee.

This was a fitting start and would theoretically explain how the infection could be transmitted except for one main thing: how the Chinese couple transmitted the virus when they showed no signs of illness.

On top of that there was a bigger mystery. It was confirmed that the third injured Singaporean woman, aged 52, had never attended that prayer. The woman attended another event at the same church later that day, so how did she catch the virus?

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Unexpected clues

Investigators resorted to examining internal camera recordings from the church that day for clues. The surprise was something unexpected. It turns out that the woman who attended the last prayer had sat in the seats that the Chinese couple had used several hours earlier.

Somehow, even though they both had no symptoms and didn't feel sick, the husband and wife managed to spread the virus. Perhaps the virus was present on their hands and they touched the seats. Perhaps their breath carried the infection, so the virus spread to a surface in the church. We don't fully know that, but it had major repercussions.

For Dr. Lee to understand how the virus was transmitted and relate events, there was only one possible explanation, which was that the virus was being transmitted by people without their knowledge. This finding has global significance because the central message of all health advice given to public opinion around the world has always been to look out for symptoms in you and others.

But if the virus is also spread by asymptomatic people silently and discreetly, how can the spread of the virus be stopped? Lee remembers that moment when he was in his office and found out the truth.

“Every time we make a scientific discovery, we live the moment when the ancient Greek scholar Archimedes cried “Eureka,” meaning I knew it, and it is the fruit of the hard work of many individuals and teams.”

Spread before symptoms appear

What was discovered has become known as “pre-symptomatic spread”, where a person does not know that he is infected because the symptoms of cough, fever and other common symptoms have not yet appeared.

This study highlighted a critical period ranging from 24 to 48 hours before the symptoms of the disease appear on patients, during which they can be a source of infection to others to a large extent, and may be the most severe sources of infection.

Knowing this fact is invaluable, because once you realize you're sick, everyone you've been in close contact with can be warned to stay home.

This means that they will be isolated during the main stage of infection before they start showing symptoms of the disease. But how the disease can be transmitted without coughing up droplets containing the virus is under debate.

One explanation is that breathing or talking to someone leads to transmission of the virus. If the virus is multiplying in the upper part of the respiratory system at that time, it is likely that some viruses will come out with each exhale. Anyone close enough, especially in hanging places, can pick it up easily.

Another method of transmission is touch - where the virus gets on someone's hands and touches another person, a doorknob or a church chair, for example. Regardless of the path the virus takes, it is evident that it takes advantage of people's inattention and lack of caution when they are not aware that they are vulnerable.

Some don't show symptoms at all

This scenario is much more puzzling and scientists simply do not have a definitive answer to it. Recognizing the fact that some people can be contagious before they have symptoms is one thing and being infected without showing any symptoms is quite another.

This condition is known as "asymptomatic" because you are a carrier but you are not suffering in any way on your own. The most famous example is the Irish cook, Mary Mallon, who was working in New York at the beginning of the last century.

Wherever Mary Mallon worked, people contracted typhoid and at least three patients, perhaps more, died without her being affected at all. Eventually it was ascertained that it was related to the disease and that it spread the disease without her knowledge.

Journalists dubbed her "Typhoid Mary", a nickname that angered her, but authorities were firm and held her in custody for 23 years until her death in 1938.

undermining hypotheses

Nurse Amelia Powell was shocked to discover that she had no symptoms of the disease. She was working in a ward at Addenbrooke's Hospital in Cambridge last April when a doctor called her to give her the result of a coronavirus swab test.

She was feeling normal and safe in the personal protective equipment she had to wear while caring for patients with the virus, but suddenly that dissipated and all those hypotheses collapsed after testing showed she had the virus.

"It was a bit like hearing that someone in your family had died, it was unbelievable," says Amelia, 23. "It can't be true, it's not me, I'm perfectly healthy," says 23-year-old Amelia. ".

She had to quit her job immediately and isolate herself at home.

“I was worried because I saw the frightening side of the disease and saw with my own eyes that the patients’ conditions deteriorated very quickly, so I wondered if I would face the same fate.” To her surprise, she did not feel at any point in her health deteriorating. "I literally had nothing, I was exercising at home, eating normally and sleeping normally."

At the moment it is impossible to know how many infections there are while they are out of sight.

Amelia's infection was detected only because she was included in a study of all hospital staff. The study showed a surprising result: up to 3% of more than 1,000 people tested positive and had no symptoms of the disease when they were tested.

A higher proportion of asymptomatic cases were also found on the Diamond Princess cruise ship, which was sailing off the coast of Japan earlier this year, with 700 cases of the virus on board.

The researchers found that three-quarters of those who tested positive for the infection had no symptoms.

In a nursing home in Washington state in the United States, half of the inmates were found to be carrying the virus, but they did not show any sign of illness.

There is no single reliable study.

Various studies indicate very different percentages of the number of people who carry the virus, but do not show any symptoms, and range from 5 to 80 percent of the number of cases. That was the conclusion of an analysis that Professor Carl Heneghan and colleagues from the University of Oxford did after examining 21 research projects.

"There is no single reliable study to determine the proportion of asymptomatic," they said. They noted that if testing for the virus was only performed on people with symptoms which is the focus of UK testing policy, a number of cases and "probably a lot of cases" would be missed.

The danger of "silent distributors of the virus"

Nurse Amelia's biggest concern was that she might have unknowingly passed the virus on either to those she works with or to patients who depend on her help.

She says, "I don't think I transmitted the virus to others because all colleagues I work with turned out to be uninfected, but thinking about how long I've been carrying the virus was a big concern for me, but we still don't know if the people who carry the virus and do not show them." Symptoms count others or not. It is very strange and the information on this matter at the moment is scarce."

One study in China found that the number of asymptomatic cases was actually greater than those with symptoms, which infuriated the authorities. The scientists said that they are silent spreaders of the disease and therefore "asymptomatic vectors should be given attention in the framework of the mission of disease prevention and control."

The team that studied the cruise ship found that the virus carriers who did not show symptoms are likely to be less likely to spread the infection than people who suffer from symptoms, but despite that, it is likely that they were the source of infection of a large number of cases.

The "dark matter" of asymptomatic infection

In an effort to find an answer, scientists in the British city of Norwich are trying to test the population of the entire city.

"It may be that asymptomatic cases are like the black substance of an epidemic," says Professor Neil Hall, head of the Earlham Institute, the life sciences research center that is leading the initiative. Dark matter is the invisible matter that is believed to make up most of the matter in the universe and has yet to be identified.

Professor Hall fears that asymptomatic cases may actually lead to the spread and persistence of the epidemic despite public health measures. "If you have people who don't know they are sick while using public transportation and healthcare facilities, that will certainly increase the spread of infection."

"Any solution that depends only on dealing with people who come to health centers when they have symptoms only addresses half of the problem."

A team of scientists in California believes that not knowing who carries the virus without showing symptoms is the "Achilles heel" (the weak point) in the fight against the epidemic.

In their view, the only way to stop the spread of the disease is to find out who is infected regardless of whether they think they are infected or not. This was also the recommendation of MPs from the House of Commons Committee on Science and Technology in their letter to Prime Minister Boris Johnson.

They wrote that the risk of asymptomatic transmission of infection to those infected had "serious consequences for epidemic control efforts." They said anyone caring for vulnerable people such as health care workers and care homes should have regular regular exams.

Such a measure is being adopted, but on a much larger scale in the Chinese city of Wuhan, where the epidemic is believed to have originated.

As many as 6.5 million people have been tested there in less than nine days in a comprehensive testing program aimed at detecting the disease, including in those without symptoms.

easing the lockdown

With the easing of lockdown measures and more people starting to use public transportation, return to work or shop, dealing with hidden risks is more important than ever. At the moment there is no way to know who among the growing crowd might be carrying the virus without their knowledge.

That's why governments around the world say it's imperative that everyone cooperates with efforts to trace an infected person's contacts with others and quickly self-isolate. They also stress that social distancing remains the best way to reduce and control the risk of an outbreak.

When this is not possible, the recommendation is to cover your face, albeit with a homemade mask.

When the US government announced this policy, the findings of the study of the epidemic outbreak were highlighted by church prayers in Singapore last January.

The logic here is that this is not about protecting yourself, it is about protecting others from you if you are infected but you don't know it.

Many health workers worry that masks may distract people from hand washing or social distancing, and may increase the risk of contamination if they are handled recklessly. But an increasing number of governments, most recently the United Kingdom, have become convinced of the benefits of masks.

Face coverings alone will not stop the epidemic, and since we still know little about transmission without symptoms, any step, no matter how small, is worth trying.

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