Coronavirus poses serious health hazards to humans and other animals. From 2002 to 2003, severe acute respiratory syndrome (sars cove 1) infected 8,000 people, with a fatal rate of ~ 10%. Since 2012, middle east respiratory syndrome (MERS) has infected more than 1,700 people, with a death rate of ~ 36%. Since 2013, porcine epidemic diarrhea coronavirus (PEDV) has swept across the United States, causing a death rate of nearly 100% in piglets and more than 10% of the US pig population in less than a year Smashed . Generally, coronaviruses cause widespread respiratory, gastrointestinal, and central nervous system diseases in humans and other animals, giving chalange to human health and causing economic losses. Coronaviruses are able to adapt to new environments through mutation and recombination with relative ease and are therefore programmed to efficiently alter host range and tissue tropism. Therefore, health hazards from coronaviruses are continuous and long-term. Understanding the virology of coronaviruses and controlling their spread has important implications for global health and economic sustainability.
Coronaviruses is Nidovirales related to Coronaviridae. They can be classified into four groups: alphacoronaviruses, betacoronaviruses, gamacoronaviruses, and deltacoronaviruses. Among them, alpha- and betacoronaviruses infect mammals, gammacoronaviruses infect avian species, and delatacoronaviruses infect both mammalian and avian species. Representative alphacoronaviruses include the human coronavirus NL63 (HCOV-NL63), porcine transmissible gastroenteritis coronavirus (TGEV), PEDV, and porcine respiratory coronavirus (PRCV). Representative betacoronaviruses include SARS-COV, Mers-Cov, Bat Coronavirus HKU4, mouse hepatitis Coronavirus (MHV), bovine coronavirus (BCOV), and human coronavirus OC43. Representative gamma-and delatacoronaviruses include avian infectious bronchitis coronavirus (IBV) and porcine deltacoronavirus (PDCV), respectively. Coronaviruses are large, enveloped, positive-stranded RNA viruses. They have the largest genome among all RNA viruses, typically 27 to 32 kb. The genome is packaged inside a helical capsid formed by nucleocapsid proteins (N) and further surrounded by an envelope. There are at least three structural proteins associated with the viral envelope: membrane protein (M) and envelope protein (E) are involved in virus assembly, while spike protein (S) mediates virus entry into host cells. Some coronaviruses also encode an envelope-associated hemagglutinin-esterase protein (He). Among these structural proteins, the spike virus forms large protrusions from the surface, giving the appearance of having a coronavirus crown (hence their name; corona in Latin means) (Figures 1B and and2A) .2A). In addition to virus entry mediation, the spike is an important determinant of viral host range and tissue tropism and a major inducer of host immune responses.
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