Coronaviruses are single-stranded positive-strand RNA viruses that do not divide segments and belong to the order of the Nestoviruses, Coronaviridae, and Orthocoronavirus subfamilies. Coronaviruses are a class of pathogens that mainly cause respiratory and intestinal diseases. They were first isolated from poultry in 1937 and were first discovered in humans in 1965. Under the electron microscope, the surface of this type of virus particles has many regularly arranged protrusions. The entire virus particle is like a crown of medieval European emperors, so it is named “coronavirus”.
In nature, coronaviruses are widespread in animals and must rely on host cells to reproduce. Coronavirus hosts are abundant and diverse. In addition to humans, they can also infect many mammals such as pigs, cows, cats, dogs, mink, camels, bats, mice, hedgehogs, and a variety of birds. Some coronavirus infections can cause zoonotic diseases.
How did the coronavirus enter the host cell? They must first attach to receptor molecules on the surface of the host cell. Coronavirus particles are enveloped on the envelope, and there are three proteins on the membrane surface: spike glycoprotein, small envelope glycoprotein and membrane glycoprotein. The spike glycoprotein, which is the protrusion of the “crown” mentioned above, is the key to the infectivity and pathogenicity of coronavirus. A spike composed of spike glycoproteins recognizes and binds to the receptor located on the surface of the host cell, just like the relationship between “key” and “gate”. Once the door of the host cell is opened, the cell is unsuspecting of the virus.
Coronaviridae is divided into 4 genera including α, β, γ, and δ. Coronaviruses of the genus α include 11 species including human coronavirus 229E, long-winged bat coronavirus 1, and porcine epidemic diarrhea virus. The β-coronaviruses include 9 types including murine hepatitis virus, fruit bat coronavirus HKU9, and severe acute respiratory syndrome (SARS) related viruses. Gamma coronavirus includes two species: avian coronavirus and beluga coronavirus SW1. The delta coronavirus includes porcine delta coronavirus (PDCoV).
At present, in addition to the 2019 new coronavirus, there are 6 known coronaviruses that can infect humans, of which 4 coronaviruses are more common in the population and have lower pathogenicity, generally only causing mild respiratory symptoms similar to the common cold Including human coronavirus 229E, human coronavirus OC43, human coronavirus NL63 and human coronavirus HKU1. There are two other coronaviruses that are more well known. They are severe acute respiratory syndrome coronavirus and Middle East respiratory syndrome coronavirus, which is what we refer to as SARS coronavirus and MERS coronavirus. They can cause serious respiratory diseases. It is a highly pathogenic new coronavirus.
According to the “New Coronavirus Infected Pneumonia Diagnosis and Treatment Program” issued by the National Health Construction Commission, the coronavirus isolated from the lower respiratory tract of unexplained pneumonia patients in Wuhan this time is a new coronavirus belonging to the genus β. Although the 2019 new coronavirus belongs to the same family of coronaviruses as SARS and MERS coronaviruses, their genetic characteristics are significantly different from them. The source of infection seen so far is mainly pneumonia patients infected with new-type coronary pneumonia. The transmission of droplets through the respiratory tract is the main route of transmission, and can also be transmitted through contact.