CORONA VIRIDAE-Properties of Coronaviridae

                                                          

 

CORONA VIRIDAE-INTODUCTION

The family Coronaviridae embraces over a dozen major host-specific pathogens of mammals and birds, displaying tropism for the respiratory tract (e.g., avian

infectious bronchitis virus), the enteric tract (transmissible gastroenteritis virus

of swine), or the liver and brain (murine hepatitis virus). 

No convincing evidence has yet been obtained tmo link I-rurnan coronaviruses with serious

disease affecting any of these systems, but they are an important cause of that trivial but annoying disease, the common cold. 

In addition, particles morphologically

resembling coronaviruses are often seen by electron microscopy in feces, but it has yet to be established whether they cause gastroenteritis in humans. Corona viruses have the largest genome of all the RNA viruses and exhibits a unique transcription strategy of considerable interest to molecular

biologists.

Coronaviruses are a group of related RNA virus that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the common cold(which is also caused by other VIRUSES, predominantly RHINOVIRUSES), while more lethal varieties can cause SARS,MARS and COVID 19.

 

In cows and pigs they cause diarrhea, while in mice they cause  hepatitis and encephalomylitis. America Arthur Schalk and M.C. Hawn in 1931 made the first detailed report which described a new respiratory infection of chicken in North dakota. The infection of new-born chicks was characterized by gasping and listlessness with high mortality rates of 40–90%. Leland David Bushnell and Carl Alfred Brandly isolated the virus that caused the infection in 1933.The virus was then known as infectious bronchitis virus (IBV). Charles D. Hudson and Fred Robert Beaudette cultivated the virus for the first time in 1937. 

The specimen came to be known as the Beaudette strain. In the late 1940s, two more animal coronaviruses, JHM that causes brain disease (murine encephalitis) and mouse hepatitis virus (MHV) that causes hepatitis in mice were discovered. It was not realized at the time that these three different viruses were related.

The family Coronaviridae comprises a monogeneric group of 11 viruses which infect vertebrates. The main characteristics of the member viruses are: (i) Morphological: Enveloped pleomorphic particles typically 100 nm in diameter (range 60-220 nm), bearing about 20 nm long club-shaped surface projections, (ii) Structural: A single-stranded infectious molecule of genomic RNA of about (5-7) x 10° molecular weight. A phosphorylated nucleocapsid protein [mol.wt. (50-60) x 103] complexed with the genome as a helical ribonucleoprotein; a surface (peplomer) protein, associated with one or two glycosylated polypeptides [mol.wt. (90-180) x 103]; a transmembrane (matrix) protein, associated with one polypeptide which may be glycosylated to different degrees [mol.wt. (20-35) x 103]. (iii) Replicative: Production in infected cells of multiple 3' coterminal subgenomic mRNAs extending for different lengths in the 5' direction. 

Virions bud intracytoplasmically. (iv) Antigenic: 3 major antigens, each corresponding to one class of virion protein, (v) Biological: Predominantly restricted to infection of natural vertebrate hosts by horizontal transmission via the fecal/oral route. Responsible mainly for respiratory and gastrointestinal disorders.