Here’s what coronavirus does to the body - National Geographic UK

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 off the infected tissue in a bid to save the rest of the body.

Humans rely on our immune systems to keep their cool when facing a threat. But during a runaway coronavirus infection, when the immune system dumps cytokines into the lungs without any regulation, this culling becomes a free-for-all, Rasmussen says “Instead of shooting at a target with a gun, you’re using a missile launcher,” she says. That’s where the problem arises: Your body is not just targeting the infected cells. It is attacking healthy tissue too.

The implications extend outside the lungs. Cytokine storms create inflammation that weakens blood vessels in the lungs and causes fluid to seep through to the air sacs. “Basically you’re bleeding out of your blood vessels,” Rasmussen says. The storm spills into your circulatory system and creates systemic issues across multiple organs.

From there, things can take a sharp turn for the worse. In some of the most severe COVID-19 cases, the cytokine response—combined with a diminished capacity to pump oxygen to the rest of the body—can result in multi-organ failure. Scientists don’t know exactly why some patients experience complications outside of the lung, but it might be linked to underlying conditions like heart disease or diabetes.

“Even if the virus doesn’t get to kidneys and liver and spleen and other things, it can have clear downstream effects on all of those processes,” Frieman says. And that’s when things can get serious.

Liver: Collateral damage

When a zoonotic coronavirus spreads from the respiratory system, your liver is often one downstream organ that suffers. Doctors have seen indications of liver injury with SARS, MERS, and COVID-19—often mild, though more severe cases have led to severe liver damage and even liver failure. So what’s happening?

“Once a virus gets into your bloodstream, they can swim to any part of your body,” Lok says. “The liver is a very vascular organ so [a coronavirus] can very easily get into your liver.”

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

In a normal body, Lok explains, liver cells are constantly dying off and releasing enzymes into your bloodstream. This resourceful organ then quickly regenerates new cells and carries on with its day. Because of that regeneration process, the liver can withstand a lot of injury.

When you have abnormally high levels of enzymes in your blood, though—as has been a common characteristic of patients suffering from SARS and MERS—it’s a warning sign. It might be a mild injury that the liver will quickly bounce back from or it could be something more severe—even liver failure.

Lok says scientists don’t completely understand how these respiratory viruses behave in the liver. The virus might be directly infecting the liver, replicating and killing off the cells itself. Or those cells might be collateral damage as your body’s immune response to the virus sets off a severe inflammatory reaction in the liver.

Either way, she notes that liver failure was never the sole cause of death for SARS patients. “By the time the liver fails,” she says, “often you’ll find that the patient not only has lung problems and liver problems but they may also have kidney problems. By then it becomes a systemic infection.”

Kidney: It’s all connected

Yes, your kidneys are caught up in this mess, too. Six percent of SARS patients—and a full quarter of MERS patients—suffered acute renal injury. Studies have shown the novel coronavirus can do the same. It may be a relatively uncommon feature of the disease, but it is a fatal one. Ultimately 91.7 percent of SARS patients with acute renal impairment died, according to a 2005 study in Kidney International.

Like the liver, your kidneys act as a filter your blood. Each kidney is filled with about 800,000 microscopic distilling units called nephrons. These nephrons have two main components: a filter to clean the blood and a little tubes that return the good stuff back to your body or send the waste down to your bladder as urine.

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

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

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Here’s what coronavirus does to the body - National Geographic UK
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