The current pandemic caused by novel corona virus emerged from Wuhan in China. The World Health Organization declared the illness resulting from the new virus, COVID-19 (now named SARS-CoV-2), a Public Health Emergency of International Concern. Previous viral outbreaks of Severe Acute Respiratory Syndrome (SARS) from 2002-2004 and Middle East Respiratory Syndrome (MERS) in 2012 were caused by different corona viruses.
CORONA VIRUS FAMILY
Corona viruses have been reported to cause a large variety of diseases in animals, including severe disease in livestock and domestic such as pigs, cows, chickens, dogs and cats. Transmissible Gastroenteritis in young piglets (TGEV), nervous system infection (PEDV), causing encephalitis, vomiting and wasting in pigs, feline infectious peritonitis (FIPV) in cats. Bovine CoV, Rat CoV, and Infectious Bronchitis Virus (IBV) cause mild to severe respiratory tract infections in cattle, rats, chickens, and ruminants like elk, deer and camels respectively. Bat CoVs, are the likely ultimate source for SARS-CoV and MERS-CoV.
NOVEL CORONA VIRUS RESEARCH
The SARS-COV-2 is a spherical virus which carries genetic information in large RNA molecule. It is called CORONA virus because of crown like club shaped protein spikes protrude from the outer edge of the virus particle. The scientists in China have released the sequence of genome of SARS-COR2 that codes for structural proteins. Drs. A.R. Fehr and S. Perlman from the University of Iowa Carver College of Medicine have reported Coronavirus particles contain four main structural proteins: the spike (S), membrane (M), envelope (E), and nucleocapsid (N) proteins, all of which are encoded within the viral genome. S spike proteins bind to host cells.
The researchers used cryo-electron microscopy to take detailed pictures of the structure of the spike protein by freezing virus particles and firing a stream of high-energy electrons through the sample to create tens of thousands of images. The researchers found that the SARS-CoV-2 spike was 10 to 20 times more likely to bind ACE2 on human cells than the spike from the SARS virus from 2002. This may enable SARS-CoV-2 to spread more easily from person to person than the earlier virus.
S spike protein binds to receptors on the human cell surface called angiotensin-converting enzyme 2 (ACE2). A collaborative team of scientists including Dr. Jason McLellan, at the University of Texas and the NIAID Vaccine Research Center (VRC) isolated a piece of the genome sequences predicted to encode for its spike protein, an important step for large scale production of proteins for vaccine development.
Following receptor binding, the virus next gains access to the host cell cytosol. This is generally accomplished by acid-dependent proteolytic cleavage of S protein by a cathepsin (protein cleaving enzyme). The next step in the corona virus lifecycle is the translation of the replicase gene from the virion genomic RNA.
Following assembly, virions are transported to the cell surface in vesicles and released by exocytosis. S protein that does not get assembled into virions transits to the cell surface where it mediates cell-cell fusion between infected cells and adjacent, uninfected cells. This leads to the formation of giant, multinucleated cells, which allows the virus to spread within an infected organism without being detected or neutralized by virus-specific antibodies.
VACCINE OR CONTROL PERSPECTIVES
There are a few important issues why it is difficult to control this virus. One is its ability to bind host cells 10-20 times more likely than SARS and MERS CORONA viruses resulting in rapid spread from person to person. Second is its covert ability to infect internally from cell to cell hiding from circulating antibodies. Third is its inflammatory manifestation in multiple organs causing rapid fatality. Since it resembles influenza viruses in its structural vulnerability to simple sanitizing and chemical agents, the best way to control is prevention through social distancing and limiting its spread through sanitizing and disinfecting body and inanimate surfaces.