The genetic material of this virus showed many similarities to SARS-CoV (79.5%) and bat coronaviruses (96%). This means the virus may have originally come from bats. Scientists did more experiments that showed the virus probably went from bats to an intermediate host, meaning another animal in between bats and humans. The viruses in that other animal changed over time until they could infect humans. Scientists are close to sure that the original animal was a bat but not sure what the intermediate animal was. Some scientists think it could have been a pangolin because there are coronaviruses that live in pangolins even though they are not exactly the same as SARS-CoV-2 or the ones in bats. Pangolins are an endangered species and buying, selling or moving them from place to place is illegal in China and many other countries. But their scales are an ingredient in many traditional Chinese medicines, so they are often sold on the black market.
Although SARS-CoV-2 began in bats, scientists noticed that the bats do not get sick and die from it. They think this is because the bats have very careful immune systems that fight the virus without causing inflammation. Scientists are studying bats because of this.
Scientists are still looking at SARS-CoV-2 infection in animals, but only a variant strain has been confirmed to spread to minks which has become a huge problem worldwide. It is also inducing fear in humans as there are cases being reported of transmission of COVID-19 from minks to humans. Cats, dogs and other mammals are said to at relative risk but how they can get infected is still a mystery.
In early February 2020, the International Committee on the Taxonomy of Viruses' Coronavirus Study Group gave SARS-CoV-2 its official name, for sudden acute respiratory syndrome coronavirus number two. Before that, people called the virus "2019-nCoV," for "novel (new) coronavirus that appeared in 2019." The study group chose this name because the new virus was so similar to another virus that was already called SARS-CoV with no number.
First, the virus enters the cell with the help of the S protein or spike protein expressed on the surface of the virus beyond its envelope. The spike protein attaches to the human cell receptor hACE2 or human angiotensin-converting enzyme 2 "." ACE2 is found on the cells of the epithelial cell linings of the lungs, kidneys, and intestines. After the attachment of the S- protein to the virus, the S protein splits into its two components- S1 head and S2 stalk . The S1 head is now able to bind to the TMPRSS2 receptor which is a serine protease enzyme containing a transmembrane domain. The interaction of TMPRSS2 and S1 trigger the cell membrane of the human cell to merge with that of the virus leading to viral genome entry into cells via endosomes. The viral genome in the endosomes which convert to lysosomes is then processed by , which is then replicated in the human cells and released after viral packaging and maturation in the cells to infect others. In October 2020, scientists said they had seen SARS-CoV-2 use another receptor, , to enter cells with the help of the furin cleavage site in its genome which was not found in any of its previous ancestors.
SARS-CoV-2 can infect many kinds of cells, but it mostly infects cells in the respiratory system, such as the cells of the nose, pharynx and lungs. Because it is in cells inside the nose, it can spread via aerosol or droplets when people breathe, talk, cough or sneeze.
The expanding part of the lungs, pulmonary alveoli, have two main types of cells. One cell, type I, absorbs oxygen from the air, i.e. gas exchange. The other, type II, produces surfactants, that help keep the lungs fluid, clean, infection free, etc. COVID-19 finds a way into a surfactant producing type II cell, and smothers it by reproducing COVID-19 virus within it. Each type II cell which is killed by the virus causes an extreme reaction in the lungs. Fluids, pus, and dead cell material flood the lung, causing the coronavirus pulmonary disease.
Scientists looked at the lungs from people who died of COVID-19. They compared them to lungs from people who died of influenza A and to lungs from people who died but not from any problem with their lungs. They saw the cells that made up the skins of the blood vessels in the lungs were more badly damaged in the lungs from COVID-19 patients, and there was more blood clotting. The most important difference the scientists saw was that the lungs had begun to grow new blood vessels.
In February 2020, the World Health Organization announced they had chosen a name for the disease caused by SARS-CoV-2: COVID-19. "Covi" for "coronavirus," "D" for "disease," and "19" for the year 2019. They said they did not want the name to have any person, place, or animal in it, like "Wuhan," or “pangolin,” because then people might blame the disease on that place, person, or animal. They also wanted the name to be easy to say out loud.
According to the United States Centers for Disease Control and Prevention, COVID-19 makes people feel sick in different ways, but it usually affects the lungs. People usually cough and have difficulty breathing. They often also have a fever, chills, headache, pain in their muscles, or trouble tasting or smelling things.
According to an April 2020 study by the American Gastroenterological Association, COVID-19 can make sick people vomit or have diarrhea but this is rare. They said about 7.7% of COVID-19 patients threw up, about 7.8% had diarrhea and about 3.6% had pain in their stomachs.
A study from the University of Arizona found that SARS-CoV-2 can prevent an infected person from feeling pain. It does this by giving off vascular endothelial growth factor-A, which binds to the human body's neuropilin receptor. This way, sick people do not feel pain, do not know they are sick, and spread the virus more than if they could feel pain.
The SARS-CoV-2 virus looks like a round ball with spikes all around it. There are four parts to the virus: the spikes, a membrane, an envelope, and the virus' genetic material, or ribonucleic acid (RNA) Each of these four parts is a different protein molecule. The spikes, membrane, and envelope are together called the "viral envelope", or outer layer, of the virus.
SARS-CoV-2 is a "positive-strand" RNA virus, meaning that it uses ribonucleic acid (RNA) to hold the patterns to make the proteins it needs instead of using DNA the way humans and other multicellular living things do.
In early 2020, some people began to think that the SARS-CoV-2 may have been made on purpose in a laboratory at the Wuhan Institute of Virology and released in Wuhan like a weapon. When the leader of Iran, Ayatollah Khamenei, said that he did not want the United States to help his country against coronavirus, he named the idea that Americans had made the virus on purpose to harm Iranains as one of his reasons: "I do not know how real this accusation is but when it exists, who in their right mind would trust you to bring them medication?" said Khamenei.
One survey by Pew Research showed 29% of Americans who answered thought SARS-CoV-2 could have been made in a lab on purpose and 23% thought it could have been made in a lab by accident. A survey of people in the United Kingdom showed many of them thought COVID-19 was caused by 5G wireless networks.
On March 17, 2020, scientists from Columbia University and other places published a paper in "Nature Medicine" showing that SARS-CoV-2 was almost surely not made by humans in a laboratory. They did this by comparing the genomes of different viruses to each other. The scientists saw that SARS-CoV-2 did not match any of the viral backbones that already exist for virologists to use. The paper in "Nature Medicine" soon became one of the most cited scientific papers of all time.