Since December 2019, a continuous series of unexplained pneumonia cases have been reported in Wuhan, China. At the beginning of the year 2020, the World Health Organization
(WHO) named the disease as coronavirus disease 2019 (COVID‐19). Coronavirus is typically found in avian and mammalian species. They are similar to each other in morphology and chemical structure. To date, there is no study that proves the disease can be transmitted by animals. In humans, the disease is observed to cause mild upper respiratory infections, but in rare cases, gastrointestinal infection is also reported with mild diarrhea in children.
Coronavirus virions are spherical to pleomorphic enveloped particles. This envelope is embedded with glycoproteins surrounding a core consisting of matrix proteins, which contains a strand of positive-sense RNA associated with the nucleoprotein. The embedded glycoproteins are responsible for the attachment to the host cell carrying the main antigens recognized by the neutralizing antibodies.
Coronavirus was originally classified under the family Coronaviridae due to its crown-like appearance by the embedded glycoproteins. Most coronavirus cases fall under the categories 229E-like and OC43-like. These two differ in both antigenic properties and culturing requirements. 229E like virus can be isolated in human embryogenic fibroblast cultures; OC43-like virus can be isolated or adapted to grow in suckling mouse brain.
Several research papers, state that the COVID-19 virus enters the human through specific receptors. Once entered, the virus enters the host cell and uncoats. The replication starts when the genome is transcribed and translated. A unique feature absorbed during replication is that all mRNA form a “nested set” with a 3′ end, and only the unique 5′ ends are translated. A number of 7 mRNAs are produced and the shortest mRNAs code for the nucleoprotein, the others direct the further synthesis of the genome. The proteins are later assembled at the cell membrane and the genomic RNA is integrated as a mature particle formed by the budding from internal cell membranes.
Studies conducted in both human studies and organ cultures show that coronaviruses are extremely squeamish and grow specifically in respiratory epithelial cells. Infected cells show damaged cilia, and form syncytia. Cell damage triggers inflammatory mediators stimulating sneezing, obstructing the airway and also raise the temperature of the mucosa.