From 'happy hypoxia' to purpuric rashes — here are all the perilous ways the coronavirus attacks the body

It's been almost eight months since Chinese scientists identified the coronavirus and doctors are still discovering new symptoms that can ravage the body and leave lasting damage months after recovery. 

While more than 813,000 people have died from the disease, most of the more than 23.6 million people with confirmed infections have recovered. But it hasn't affected all of them the same. Once thought of as just a respiratory illness, Covid-19 is marked as much by the variety of potentially perilous ways it harms the body as it is for the signature pneumonia it often causes, alarming doctors and public health officials. 

Because the coronavirus attacks a variety of cells in the body, there isn't one thing that connects every symptom or one treatment that seems to help every case. 

Doctors know Covid-19 can be unpredictable, stressing virtually every system in the body, including the heart, kidneys and brain. Some patients may suffer long-lasting nerve damage that impacts their ability to walk or smell, while others have continuous coughing fits and struggle to breathe, scientists and health officials say. 

"We have to come to grips that Covid might kill me, but it could also debilitate you over a significant period of time. And therefore we have to take it seriously," Dr. Mike Ryan, executive director of the World Health Organization's health emergencies program, said during a Q&A on July 29. "We have to take protecting ourselves and protecting others seriously. At some level, we have the right to potentially risk harm to ourselves. We have no right to risk harm to others."

Below is a look at what we know the coronavirus does to the body:

Researchers say symptoms can vary depending on the severity of the disease. According to an early estimate from the WHO, about 80% of Covid-19 cases are either mild or asymptomatic, meaning the person never develops symptoms. 

The most common symptoms among people who are not hospitalized with Covid-19 are dry cough, tiredness and fever, according to the WHO. Some patients may have muscle or body aches, a headache, nasal congestion, runny nose or sore throat, the agency said. Many people also experience symptoms such as nausea, vomiting or diarrhea, sometimes prior to developing a fever, according to the Centers for Disease Control and Prevention.

Because the virus attacks the lungs, people can experience shortness of breath or difficulty breathing. Some people with Covid-19 have even left hospitals healthy, only to experience coughing fits and problems breathing 10 or 15 weeks later, Ryan has said. 

In severe cases, patients may catch pneumonia, a serious illness that kills about 50,000 people in the United States each year, according to the CDC. People with pneumonia may also have acute respiratory distress syndrome, a life-threatening injury that causes fluid to fill the lungs, restricting air. The percentage of deaths attributed to pneumonia and influenza rose sharply earlier in the year, increasing to 8.2%, according to a CDC report in April. The surge likely reflects deaths associated with Covid-19, the agency said.

Multisystem Inflammatory Syndrome in Children, or MIS-C, is a rare inflammatory condition found in kids with Covid-19 that's similar to Kawasaki syndrome. In April, the WHO said it was investigating the mysterious disease after hearing about several reports of kids, many of whom had tested positive for Covid-19, being hospitalized with fever and swollen arteries. Some had died.

Health officials are still learning what connection Covid-19 has with the condition, which can inflame different parts of the body including the heart, lungs, kidneys, brain, skin, eyes and gastrointestinal organs, according to the CDC. Symptoms can include abdominal pain, vomiting, diarrhea, neck pain, a rash, bloodshot eyes and fatigue, according to the CDC. Severe complications like cardiac dysfunction, shock and injury to the kidneys can occur in some cases, according to the CDC.

It can appear in children at any time, often occurring one to six weeks following infection, according to University of Buffalo researchers. Reported cases show that Black, Hispanic and Asian children might be disproportionately affected, according to a paper in the Lancet. 

In April, the CDC added a sudden loss of taste or smell to its list of common indicators of coronavirus infection. But long before the CDC's disclosure, doctors had been warning that some patients infected with the virus were reporting problems.

People often experience the symptoms during the early stages of the disease, according to the WHO. A research team at King's College London in April identified a loss of taste and smell as one of the best ways to detect whether someone has Covid-19 after analyzing responses of more than 400,000 people who had one or more suspected symptoms of the disease. The results said that 59% of those who tested positive for the virus reported a loss of taste and smell. 

The symptoms are not uncommon with other viral infections. Researchers say many viruses, such as ones that cause the common cold or flu, can cause taste and smell loss because of congestion. However, researchers in Britain noted the symptoms may be more severe in people who have Covid-19. That may be due to the way the coronavirus impacts the brain and nervous system, they said, adding it may impact different mechanisms in the body responsible for taste and smell.

A coronavirus infection may also trigger rashes or hives, according to dermatologists in a study published Aug. 5 in JAMA Dermatology. 

Researchers in New York looked at four patients who were admitted to the hospital with severe forms of Covid-19 from March 13 to April 3. They found skin was discolored and had retiform purpura, a type of lesion. The researchers said the findings could be a sign of blood clots.

"The findings suggest that clinicians caring for patients with COVID-19 should be aware of livedoid and purpuric rashes as potential manifestations of an underlying hypercoagulable state," the researchers wrote in the paper. "If these skin findings are identified, a skin biopsy should be considered because the result may guide anticoagulation management." 

Some patients who have long recovered from coronavirus infection say they now have difficulty concentrating and are sometimes confused, according to a study of 60 patients.

The study, published in the medical journal Lancet earlier this month, compared MRIs of Covid-19 patients with those who did not have the infection. It found the patients with Covid-19 had structural changes in the brain that correlated with memory loss three months after testing positive. "This requires attention since even if the patients recover well from the pneumonia condition, the neurological changes may cause a great burden," the researchers said.

Doctors have found that Covid-19 can cause damage to the heart, sometimes leading to heart failure.

A study published in JAMA Cardiology in March looked at 416 patients hospitalized with Covid-19 between Jan. 20 and Feb. 10 and found 19.7% showed signs of cardiac injury. Patients with cardiac injury in the study were often elderly and had preexisting conditions, including hypertension. A separate study published in JAMA Cardiology in July examined MRIs from 100 people who recovered from Covid-19. They found 78 of them had heart abnormalities and 60 had signs of inflammation.

Researchers say the coronavirus appears to be capable of attacking the heart's muscle tissue as well as the receptors that help protect heart cells. The virus can put stress on the body, impacting the body's ability to pump blood effectively or carry oxygen. The body's own immune response from the virus may also cause damage to the heart.

Covid-19 patients, including young people who were otherwise healthy, may be at risk of blood clots and stroke, according to an observational study published in Neurosurgery in June.

Researchers at Thomas Jefferson University in Philadelphia, in collaboration with NYU Langone Medical Center, analyzed 14 patients who had strokes and tested positive for Covid-19 from March 20 until April 10. They said 42% of the patients studied were under age 50 even though most strokes in the U.S. occur in people over age 65.

"We were seeing patients in their 30s, 40s and 50s with massive strokes, the kind that we typically see in patients in their 70s and 80s," said Dr. Pascal Jabbour, a neurosurgeon at Jefferson's Vickie and Jack Farber Institute for Neuroscience. "Stroke is occurring in people who don't know they have COVID-19, as well as those who feel sick from their infections."

While the observational study was preliminary, Jabbour speculated the virus could be interfering with a receptor in the body that controls blood flow to the brain. 

Covid-19 can also cause long-term kidney damage, including kidney failure and death, according to the WHO.

The American Society of Nephrology, a U.S.organization focused on kidney disease, reported that 20% to 30% of patients hospitalized with a coronavirus infection develop kidney failure that requires dialysis.

The kidney damage may be a result of tiny clots that form in the bloodstream as a result of Covid-19, Dr. John Sperati, a professor at the Johns Hopkins University School of Medicine, wrote in a post. Like the heart, the virus may also be infecting the cells of the kidney and damage the tissue, he said. Low oxygen levels as a result of pneumonia may also be an issue. 

Low oxygen levels in some patients may be a result of widened blood vessels in the lungs caused by Covid-19, according to a study by Mount Sinai researchers.

The researchers performed a so-called bubble study, which is a noninvasive and painless technique for stroke risk that involves injecting saline containing tiny air bubbles into a vein. Normally, the microbubbles would travel to the right side of the heart, enter the blood vessels of the lungs, and ultimately get filtered by the pulmonary capillaries, they said. However, when researchers performed the test, they found the bubbles passed through the lungs and into the brain.

"It is becoming more evident that the virus wreaks havoc on the pulmonary vasculature in a variety of ways. This study helps explain the strange phenomenon seen in some COVID-19 patients known as 'happy hypoxia,' where oxygen levels are very low, but the patients do not appear to be in respiratory distress," Dr. Hooman Poor, a pulmonologist at Mount Sinai, said in a release.