As cases of coronavirus infection proliferate around the world and governments are taking extraordinary measures to limit the spread, there is still much confusion about what exactly the virus does to people. Symptoms – fever, cough, shortness of breath – can signal any number of illnesses, from flu to streptococcus to colds. Here’s what medical experts and researchers have learned so far about the progression of this new coronavirus infection – and what they still don’t know.
The virus is spread by droplets transmitted to the air by coughing or sneezing, which people nearby can absorb through the nose, mouth or eyes. The viral particles in these droplets move quickly to the back of your nasal passages and to the mucous membranes in the back of your throat, attaching to a particular receptor in the cells from there. Coronavirus particles have doped proteins protrude from their surfaces, and these spikes cling to cell membranes, allowing virus genetic material to enter the human cell. This genetic material proceeds to “hijack the metabolism of the cell and say, in effect,” Do not do your usual work. Your job now is to help me multiply and make the virus, ”said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center in Nashville.
As copies of the virus multiply, they burst and infect neighboring cells. Symptoms often start at the back of the throat with a sore throat and a dry cough. The virus then “gradually creeps into the bronchi,” said Dr. Schaffner. When the virus reaches the lungs, their mucous membranes become inflamed. This can damage the air sacs or lung bags and they have to work harder to perform their function of supplying oxygen to the blood that circulates throughout our body and removing carbon dioxide from the blood so that it can be exhaled. “If you get swelling there,” it’s all the more difficult for oxygen to swim through the mucous membrane, “said Dr. Amy Compton-Phillips, clinical CEO of the Providence Health System , which included Everett Hospital in Washington, which first reported a case of coronavirus in the United States in January. The swelling and decreased oxygen flow can cause these areas of the lungs to fill with fluid, pus, and dead cells. Pneumonia, a lung infection, can occur; some people have such a hard time breathing that they need to be ventilated. In the worst cases, known as acute respiratory distress syndrome, the lungs fill with so much fluid that no respiratory aid can help, and the patient dies.
What path does the virus take in the lungs?
Dr. Shu-Yuan Xiao, professor of pathology at the University of Chicago School of Medicine, has reviewed pathology reports from patients with coronavirus in China. He said the virus appears to start in the peripheral areas on both sides of the lung and may take a long time to reach the upper respiratory tract, trachea and other central respiratory tract. Xiao, who is also director of the Center for Pathology and Molecular Diagnostics at Wuhan University, said that this model explains why in Wuhan, where the epidemic started, many of the first cases were not identified immediately. Chinese hospitals have not always detected infection in the peripheral lungs, so some people with symptoms have been sent home without treatment. “They would go to other hospitals for treatment or stay at home and infect their families,” he said. “This is one of the reasons why there has been such a spread.” A recent study by a team led by researchers from the Icahn School of Medicine at Mount Sinai found that more than half of the 121 patients in China had normal CT scans at the start of their illness. . This study and Dr. Xiao’s work show that as the disease progresses, CT scans show “frosted glass opacities”, a kind of foggy haze in parts of the lung that are evident in many types of respiratory infections viral. These opaque areas can disperse and thicken in places as the disease worsens, creating what radiologists call a “crazy tiling” pattern on the scanner.
Are the lungs the only part of the body affected?
Not necessarily. Dr. Compton-Phillips said the infection can spread through the mucous membranes, from the nose to the rectum. While the virus appears to be concentrating on the lungs, it may also be able to infect cells of the gastrointestinal system. intestinal, according to experts. . This may be the reason why some patients experience symptoms like diarrhea or indigestion. The Center for Disease Control and Prevention reports that RNA for the new coronavirus has been detected in blood and stool samples, but it is not known if the infectious virus can persist in blood or stool. Bone marrow and organs like the liver can also become inflamed, said Dr. George Diaz, section chief for infectious diseases at the Providence Regional Medical Center in Everett, Washington, whose team treated the first American patient with coronavirus. There can also be inflammation in the small blood vessels, as happened with SARS, the viral epidemic in 2002 and 2003. “The virus will actually land on organs like the heart, kidneys, liver , and can cause direct damage to these people. organs, “said Dr. Schaffner. As the body’s immune system shifts into high gear to fight infection, the resulting inflammation can cause these organs to malfunction, he said. As a result, some patients may suffer damage not only caused by the virus, but by their own immune system as it rages to fight the infection. Experts have not yet documented whether the virus can affect the brain. But scientists who have studied SARS have reported evidence that the SARS virus could infiltrate the brain in some patients. Given the similarity between SARS and Covid-19, the infection caused by the new coronavirus, an article published last month in the Journal of Medical Virology argued that the possibility that the new coronavirus could infect certain nerve cells does not should not be excluded. .
Why do some people get very sick, but most don’t?
About 80% of people infected with the new coronavirus have relatively mild symptoms. But about 20% of people fall seriously ill and, in about 2% of patients in China, who has had the most cases, the disease has been fatal. Experts say the effects seem to depend on the strength or weakening of a person’s immune system. . Seniors or those with underlying health conditions, such as diabetes or another chronic disease, are more likely to develop severe symptoms. Xiao performed pathological examinations of two people in China who went to a hospital in Wuhan in January for a different reason – they needed surgery for early-stage lung cancer – but whose records have later showed that they also had a coronavirus infection, which the hospital did not do. recognize at the time. None of the lung cancer patients had advanced enough to kill them, he said, one of the patients, an 84-year-old woman with diabetes, died of pneumonia caused by a coronavirus. , said Dr. Xiao. The 5-year-old was somewhat healthier with a history of hypertension that he had managed well for 20 years. Dr. Xiao said the man had undergone surgery to remove a lung tumor, that he was released and that he returned to the hospital nine days later because of a fever and a cough deemed to be coronavirus. Xiao said the man was almost certainly infected during his first hospital stay, as other patients in his post-surgical recovery room were later found to have coronavirus. Like many other cases, it took man days to show respiratory symptoms. The man recovered after 20 days in the infectious diseases unit of the hospital. Experts say that when patients like this recover, it’s often because supportive care – fluids, breathing assistance, and other treatments – allows them to survive the worst effects of inflammation caused by the virus.
Many. Although the disease is similar in many ways to SARS and has something in common with influenza and pneumonia, the course of a patient’s coronavirus is not yet fully understood. Some patients may remain stable for longer than a week and then suddenly develop pneumonia, said Dr. Diaz. . Some patients seem to recover but develop symptoms again. Xiao said that some patients in China recovered but fell ill again, apparently because they had damaged and vulnerable lung tissue, which was later attacked by bacteria in their bodies. Some of these patients ended up dying from a bacterial infection, not the virus. But that does not seem to have caused the majority of the deaths, he said. Other cases have been tragic mysteries. Dr. Xiao said that he personally knew a man and a woman who had been infected, but appeared to be improving. Then the man deteriorated and was hospitalized. “He was in the ICU, receiving oxygen, and he texted his wife that he was fine, he had a good appetite and so on,” said Dr. Xiao. “But in the late afternoon, she stopped receiving text messages from him. She did not know what was going on. And at 10 p.m., she received notification from the hospital that he had died. “
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