The coronavirus pandemic originated in China in late 2019 as a cluster of mysterious cases of pneumonia.
The culprit was found to be a new type of virus, now called severe respiratory syndrome coronavirus 2, or SARS-Cov-2.
The virus, and the disease it causes — COVID-19 — is fatal to a small percentage of the people it affects. Most of the danger is related to pneumonia, or an inflammation of the lungs caused by infection, although there is still much uncertainty about how the viral infection spreads and progresses in the body.
The early symptoms are usually a cough, fever and shortness of breath, and look a lot like the flu or common cold. Symptoms appear 2-14 days after exposure, the Centers for Disease Control said.
The virus circulates through droplets in the air spread by coughing or sneezing, and enters the body through the mouth, eyes or nose. It can remain viable on surfaces for hours to days, and may be able to enter the lungs directly when inhaled.
After entering the body, the virus spreads to the back of the nasal passage and to mucous membranes in the throat, attaching to the body’s cell receptors.
The viral particles hook onto the outer walls of the host’s cells, the virus’s genetic material breaches the cell membrane, and it then hijacks the cell into making more copies of the virus. The virus copies proliferate, break out of the cell, and infect other cells in the body. A single cell can churn out millions of copies of the virus before it dies.
The virus then moves from the back of the throat down the bronchial tubes toward the lungs, according to a report from The New York Times based on interviews with leading experts in infectious diseases.
The infection can then reach the lungs, causing inflammation in their mucous membranes and damaging their air sacs. The inflammation hampers the lungs’ ability to oxygenate the blood and remove carbon dioxide from the bloodstream.
The inflammation in the lungs, and their reduced efficacy, can cause them to fill with fluids, pus and dead cells, and cause an infection, leading to pneumonia.
Some people who are infected have difficulty breathing and require a ventilator, and for others, the lungs become so inundated with fluids that even with intervention, they die.
People suffering from pneumonia are also at a heightened risk for secondary viral and bacterial infections.
Pneumonia caused by the coronavirus appears to be more severe than most cases of the disease, and affects a greater portion of the lungs, experts told The Guardian newspaper. Pneumonia is usually caused by bacterial infection, which can be treated with antibiotics.
The COVID-19 lung infection appears to start on the outer parts of the sides of the lung, then moves to more central areas, including the upper respiratory tract and trachea.
The virus can also enter the bloodstream, and may be able to infect the gastrointestinal system, causing symptoms like diarrhea and indigestion. The infection can also directly damage organs including the heart, kidneys, and liver, and cause bone marrow to become inflamed. Small blood vessels may also be vulnerable to inflammation.
The body’s own immune response to the infection can cause inflammation and organ malfunction. It is still unclear if the brain is affected.
The Centers for Disease Control said the virus has been detected in blood and stool specimens, but it is unclear whether it can spread through any bodily fluids.
There are at least six other kinds of coronavirus that can infect humans. Some cause colds, while others caused the SARS and MERS outbreaks. The SARS-Cov-2 strain is believed to have originated in bats.
Health experts recommend regular hand washing to limit exposure. Soap effectively destroys the virus when it is outside the body because it dissolves the virus’s lipid bilayer, or its outer membrane made of fat, causing the viral particles to fall apart. Hand sanitizer and alcohol products are less effective than soap in combating the virus.
According to the World Health Organization, people with mild illness recover in about two weeks, while those with more severe ailments who survive may take three to six weeks to rebound.