Here’s what coronavirus does to the body

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Much remains unknown about the new coronavirus that is tearing China apart, but one thing is for sure. The disease can throw a storm all over the human body.
This has been the nature of zoonotic coronaviruses of the past, those that have jumped from animals to humans like SARS and MERS. Unlike their cousins ​​who cause colds, these emerging coronaviruses can start a viral fire in many organs of a person, and the new disease - dubbed "COVID-19" by the World Health Organization Tuesday - is no exception when it is severe.
This helps explain why the COVID-19 epidemic killed more than 1,300 people, surpassing the death toll from SARS in a matter of weeks. While the death rate for COVID-19 appears to be one-tenth of SARS, the new coronavirus has spread more quickly.

Confirmed cases Rose to more than 60,000 Thursday, a jump of almost 50% compared to the previous day. This jump reflects a change in the way Chinese authorities diagnose infections instead of a massive change in the scope of the epidemic. Rather than waiting for patients to test positive for the virus, diagnoses now include anyone whose chest CT scan reveals the distinctive pattern of COVID-19 pneumonia. We hope this method will allow authorities to isolate and treat patients more quickly.

If this epidemic continues to spread, it is unclear how it could become harmful. A prominent epidemiologist at the University of Hong Kong warned this week that COVID-19 could infect 60% of the world if it is not checked. China's National Health Commission said more than 1,700 health workers were sick with the new virus on Thursday, and the announcement came just a day after the WHO closed a summit on best protocols for hospital care and the development of therapies, such as vaccines.

But what really happens to your body when it is infected with the coronavirus? The new strain is so genetically similar to SARS that it has inherited the title SARS-CoV-2. Thus, combining the first research on the new outbreak with the lessons of SARS and MERS can provide an answer.

The lungs: Ground Zero

For most patients, COVID-19 starts and ends in their lungs because, like the flu, coronaviruses are respiratory diseases.
They usually spread when an infected person coughs or sneezes, spraying droplets that can spread the virus to anyone in close contact. Coronaviruses also cause flu-like symptoms: patients may start with fever and cough that progress to pneumonia or worse. (Find out how coronavirus spreads on a plane and the safest place to sit).

After the SARS epidemic, the World Health Organization reported that the disease has typically attacked the lungs in three phases: viral replication, immune over-reactivity, and lung destruction.

Not all patients went through all three phases - in fact, only 25% of SARS patients suffered from respiratory failure, the defining signature of severe cases. Likewise, COVID-19, according to initial data, causes milder symptoms in approximately 82% of cases, while the others are severe or critical.

Take a closer look and the new coronavirus appears to follow other models of SARS, says Associate Professor of the University of Maryland School of Medicine Matthew B. Frieman, who studies highly pathogenic coronaviruses.

Medical staff kiss in an isolation room at a hospital in Zouping, China's Shandong Province, during Easter.

Photograph of STR / AFP via Getty Images

At the very start of an infection, the new coronavirus quickly invades human lung cells. These lung cells fall into two classes: those that produce mucus and those that have hair-like batons called eyelashes.
Mucus, while coarse on the outside of the body, helps protect lung tissue from pathogens and makes sure your respiratory organ doesn't dry out. The eyelash cells beat around the mucus, removing debris like pollen or viruses.

Frieman explains that SARS liked to infect and kill the hair cells, which then evaporated and filled the patient's airways with debris and fluids, and he hypothesizes that the same thing happens with the new coronavirus. This is because early studies of COVID-19 have shown that many patients develop pneumonia in both lungs, accompanied by symptoms such as shortness of breath.

That's when phase two and the immune system come in. Awakened by the presence of a viral invader, our body mobilizes to fight the disease by flooding the lungs with immune cells to eliminate damage and repair lung tissue.

When functioning properly, this inflammatory process is tightly regulated and limited only to infected areas. But sometimes your immune system goes haywire and these cells kill everything in their path, including your healthy tissue.

"So you get more damage instead of less of the immune response," says Frieman. Even more debris clogs the lungs and the pneumonia gets worse. (Find out how the new coronavirus compares to the flu, Ebola and other major epidemics).

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In the third phase, lung damage continues to accumulate, which can lead to respiratory failure. Even if there are no deaths, some patients survive with permanent lung damage. According to the WHO, SARS has pierced holes in the lungs, making them "look like a honeycomb" - and these lesions are present in people with new coronavirus, too.

These holes are probably created by the overactive response of the immune system, which creates scars that protect and strengthen the lungs.

When this happens, patients often need to be put on ventilators to help them breathe. Meanwhile, the inflammation also makes the membranes between the air sacs and blood vessels more permeable, which can fill the lungs with fluid and affect their ability to oxygenate the blood.

"In severe cases, you flood your lungs and you can't breathe," says Frieman. "This is how people die. "

The stomach: a shared gateway

During the SARS and MERS outbreaks, almost a quarter of patients suffered from diarrhea - a much more prominent feature of these zoonotic coronaviruses. But Frieman says it is still unclear whether gastrointestinal symptoms play a major role in the latest epidemic, since cases of diarrhea and abdominal pain have been rare. But why does a respiratory virus upset the gut?
When a virus enters your body, it searches for human cells with its favorite gates - proteins outside of cells called receptors. If the virus finds a compatible receptor on a cell, it can invade.

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Some viruses are picky on the door they choose, but others are a little more promiscuous. "They can very easily penetrate all types of cells," says Anna Suk-Fong Lok, assistant dean of clinical research at the University of Michigan faculty of medicine and president-elect of the American Association for the Study liver disease.

Both SARS and MERS viruses can access the cells that line your intestines and the large and small colon, and these infections appear to thrive in the gut, potentially causing damage or fluid leakage that becomes diarrhea.

But Frieman says we don't know yet if the new coronavirus does the same. Researchers believe COVID-19 uses the same receptor as SARS, and this gate can be found in your lungs and small intestine.

Two studies — one in the New England Medical Journal and a preprint in medRxiv involving 1,099 cases — also detected the virus in stool samples, which could indicate that the virus could spread through feces. But that is far from conclusive.

"Whether this type of fecal transmission occurs for this Wuhan virus, we don't know at all," says Frieman. "But it seems to be there in the stool and it looks like people have gastrointestinal symptoms associated with it." "

Bloodstorm

Coronaviruses can also cause problems in other systems of the body, due to the overactive immune response that we mentioned earlier.
A 2014 study showed that 92% of MERS patients had at least one manifestation of the coronavirus outside the lungs. In fact, signs of a complete body blitz have been seen with the three zoonotic coronaviruses: elevated liver enzymes, decreased white blood cells and platelets, and low blood pressure. In rare cases, patients have suffered from acute kidney damage and cardiac arrest.

But that's not necessarily a sign that the virus itself is spreading throughout the body, says Angela Rasmussen, virologist and associate researcher at Columbia University Mailman School of Public Health. It could be a cytokine storm.

Cytokines are proteins used by the immune system as alarm beacons - they recruit immune cells to the site of infection. The immune cells then kill the infected tissue to save the rest of the body.

Humans rely on our immune system to keep their cool in the face of a threat. But in an uncontrolled coronavirus infection, when the immune system throws cytokines into the lungs without any regulation, this elimination becomes a freedom for everyone, Rasmussen says: "Instead of shooting a target with a gun, you use a missile launcher, "she says. This is where the problem arises: your body doesn't just target infected cells. It also attacks healthy tissue.

The implications extend outside the lungs. Cytokine storms create inflammation that weakens the blood vessels in the lungs and causes fluid to seep into the air sacs. "Basically, you're bleeding from your blood vessels," says Rasmussen. The storm spills into your circulatory system and creates systemic problems in several organs.

From there, things can get worse. In some of the more severe cases of COVID-19, the cytokine response - combined with a decreased ability to pump oxygen to the rest of the body - can result in multiple organ failure. Scientists aren't sure why some patients develop complications outside the lungs, but it could be linked to underlying conditions like heart disease or diabetes.

"Even if the virus does not reach the kidneys, liver and spleen and other things, it can have obvious downstream effects on all of these processes," says Frieman. And this is where things can get serious.

Liver: collateral damage

When a zoonotic coronavirus spreads through the respiratory system, your liver is often a downstream organ that suffers. Doctors have seen signs of liver damage with SARS, MERS and COVID-19 - often mild, but more severe cases have led to severe liver damage and even liver failure. So what's going on?
"Once a virus enters your bloodstream, it can swim to any part of your body," says Lok. "The liver is a very vascular organ so [a coronavirus] can very easily enter your liver. "

Your liver works hard enough to make sure your body can function properly. Its main job is to process your blood after it leaves the stomach, to filter out toxins and to create nutrients that your body can use. It also makes bile which helps your small intestine to break down fat. Your liver also contains enzymes that speed up chemical reactions in the body.

In a normal body, says Lok, liver cells constantly die and release enzymes into your bloodstream. This ingenious organ then quickly regenerates new cells and continues its day. Due to this regenerative process, the liver can endure many injuries.

When you have abnormally high levels of enzymes in your blood, as has been a common feature in patients with SARS and MERS - this is a warning sign. It can be a minor injury from which the liver will quickly rebound, or something more serious, even liver failure.

Lok says scientists don't fully understand how these respiratory viruses behave in the liver. The virus could directly infect the liver, replicate and kill the cells themselves. Or these cells can be collateral damage because your body's immune response to the virus triggers a severe inflammatory reaction in the liver.

In any event, she notes that liver failure has never been the only cause of death in patients with SARS. "By the time the liver breaks down," she says, "you will often find that the patient has not only lung and liver problems, but also kidney problems. By then, it becomes a systemic infection. "

Kidney: everything is connected

Yes, your kidneys are also caught in this mess. Six percent of SARS patients - and a full quarter of MERS patients - have suffered acute kidney injury. Studies have shown the new coronavirus can do the same. It may be a relatively rare feature of the disease, but it is fatal. In the end, 91.7% of SARS patients with acute kidney disease died, according to 2005 study Kidney International.
Like the liver, your kidneys act as a filter for your blood. Each kidney is filled with about 800,000 microscopic distillation units called nephrons. These nephrons have two main components: a filter to clean the blood and a small tube that returns the good things to your body or sends the waste to your bladder in the form of urine.

The kidney tubules seem to be the most affected by these zoonotic coronaviruses. After the SARS epidemic, WHO reported that the virus was found in the kidney tubules, which can become inflamed.

It is not uncommon to detect a virus in the tubules if it is in your bloodstream, says Kar Neng Lai, professor emeritus at the University of Hong Kong and consultant nephrologist at the Sanatorium and Hospital in Hong Kong. As your kidneys continually filter blood, tubular cells can sometimes trap the virus and cause a transient or lighter injury.

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This injury could become fatal if the virus enters cells and begins to replicate. But Lai, who was also a member of the first group of researchers reporting on SARS and contributed to the Kidney International study - says there was no evidence that the SARS virus replicated in the kidney.

The discovery, says Lai, suggests that acute kidney damage in SARS patients could be due to a variety of causes, including low blood pressure, sepsis, medication, or metabolic disruption. Meanwhile, the most serious cases that have led to acute kidney failure have shown signs - you guessed it - of a cytokine storm.

Acute kidney failure can also sometimes be caused by antibiotics, multi-organ failure, or connection to a ventilator for too long. Everything is connected.

Pregnancy and coronavirus?

It’s the great irony of the Twitter era that we know too little about the new coronavirus as we drown in updates about it. Medical journals have published several studies on this epidemic - some more verified than others as researchers rush to feed the mouth. Meanwhile, the media reports on each development. All of this information revolves around the Internet where discerning fact from fiction is a notorious challenge.

"This is truly unprecedented in terms of updated reports on what is going on in these studies," said Rasmussen. "It is really difficult to try to sort through all of the information and determine what is really supported, what is speculative and what is wrong. "

For example, last week, doctors at a hospital in Wuhan reported that two infants tested positive for the new coronavirus, just 30 hours after birth. Naturally, this troubling headline has spread among news outlets, as it has raised the question of whether pregnant women can infect their unborn children in utero or whether the disease can be transmitted during birth or through breast milk .

But let's break the breaks. No mother-to-child transmission has been observed with SARS or MERS despite numerous cases involving pregnant women. In addition, there are other ways in which a newborn could get the coronavirus, says Rasmussen, as if he were born in a hospital overwhelmed by infected patients during a hectic emergency.

In reality, a new study released Thursday The Lancet offers preliminary evidence that the coronavirus cannot be passed from mother to child.

In the report, the researchers observed nine women in Wuhan who had COVID-19 pneumonia. Some women have had pregnancy complications, but all cases have resulted in live births without evidence of transmission of the infection. Although this study does not completely rule out the possibility of transmission during pregnancy, it does emphasize the need for caution when speculating on this disease.

"There has to be a high level of evidence before it can be said to be happening definitively - and certainly before you start to change the way cases are handled clinically or in terms of public policy," said Rasmussen.

Frieman agrees. He hopes that this epidemic will generate more funding for research on coronaviruses such as the recent promises from the European Union and the Bill & Melinda Gates Foundation. But Frieman wants the support and interest to continue even if this epidemic eventually ends, unlike what happened with SARS research.

"Right after the SARS epidemic, there was a large sum of money and then it disappeared," said Frieman. "Why don't we have these answers? No one funded these things. "

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