HOW DOES THE PANDEMIC CORONAVIRUS (SARS-CoV-2) HIJACK THE CELLS OF AN INFECTED PERSON?

Coronaviruses (CoV) are a large family of viruses that cause illness ranging from the common cold to more severe diseases such as Middle East Respiratory Syndrome (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS-CoV). Three (3) genera in the coronaviridae family namely Alpha-coronavirus, Beta-coronavirus and Torovirus contain viruses that are able to cause human infection.

Under the first two genera, there are six (6) coronaviruses that can infect humans. Alpha- coronavirus – the strain 229E and NL63 and the Beta-coronavirus – the strain OC43, HKU1, SARS-CoV, and MERS-CoV.

STRUCTURE AND COMPOSITION

The Latin word “Corona” means “crown” which describes the projections seen around the virus when viewed under an electron microscope.

Coronaviruses are enveloped, 120 to 160 nanometer (nm) particles that contain an unsegmented genome of single-stranded positive-sense RNA of about 30 kilobases (kb), the largest genome among RNA viruses. The genome has a 5’ methylated cap and the 3’ polyadenylated tail. The helical nucleocapsid is 9 to 11 nm in diameter.

Figure 2. Shows the general structure of coronavirus (SARS-CoV-2)

There are long club- or petal-shaped projections that are widely spaced on the outer surface of the envelope. The viral structural proteins include a phosphorylated nucleocapsid (N) protein, a membrane

• glycoprotein that serves as a matrix protein embedded in the envelope lipid bilayer which interacts with the nucleocapsid and the spike (S) glycoprotein which is the petal-shaped peplomers. Some human coronaviruses, for example, the strain OC43 (HCoV-OC43) and SARS-CoV-2 contain a third glycoprotein (HE) that cause hemagglutination and has acetylesterase

The lipid bilayer envelope, membrane proteins, and nucleocapsid protect the virus when it is outside a host cell.

THE GENOMIC ORGANIZATION OF CORONAVIRUS (SARS-CoV-2)

Fig 3. Shows the genomic organization of SARS-CoV-2

The SARS-CoV-2 genome is about 30 kb. The Open Reading Frames (ORF1a and ORF1b) encode for the replicase polyproteins and the others encode for the structural and accessory proteins. The S, E, M, N within the genome encode for the Spike, Envelope, Membrane, and Nucleocapsid respectively.

Since the discovery of the novel coronavirus in December 2019 in Wuhan, several concerns have been raised about this virus (SARS-CoV-2). One of the concerns I would like to share with you is – how this virus hijack the cells of an infected person.

 HOW CORONAVIRUS (SARS-CoV-2) HIJACKS THE CELLS OF AN INFECTED PERSON?

The entire replication of coronavirus occurs in the cytoplasm of a host cell. The virus enters the body through the nose, mouth or eyes, then attaches and penetrates host cells that produce a protein (receptor) called Angiotensin-Converting Enzyme 2 (ACE2). A serine protease (TMPRSS2) of the host cell cleaves and activates the receptor-attached spike protein. Depending on the host cell protease available, cleavage and activation allow cell entry of the virus through endocytosis or direct fusion of the viral envelope with the host membrane.

On entry into the host cell, the virus uncoats and releases its viral RNA into the cytoplasm. The presence of the 5’ methylated cap and the 3’ polyadenylated tail enables the viral RNA to attach to the host cell’s ribosome for translation. The host ribosome translates the overlapping Open Reading Frames (ORF1a and ORF1b) of the viral RNA to form two replicase polyproteins (pp1a and pp1ab). These polyproteins have their own protease which cleaves them into multiple nonstructural viral proteins.

These nonstructural viral proteins are involved in replication and transcription by binding to the Sense strand (RNA (+)). When they bind to the Sense strand for replication, an Anti-Sense strand (RNA (-)) is produced. At this stage, the Anti-Sense strand (RNA (-)) can be replicated back into a Sense strand (RNA (+)) or transcribed in a method called discontinuous transcription to yield different sub-genomic sized mRNAs.

 These sub-genomic sized mRNAs are translated by the host’s ribosome into viral structural proteins (S, E, M, and N) and accessory proteins. The N protein packages the Sense strand (RNA (+)) into a nucleocapsid and is assembled into a virus particle in the rough Endoplasmic Reticulum. The newly formed virus particle undergoes maturation when passing through the Golgi bodies and exits the host cell via exocytosis.

Now that we know how the SARS-CoV-2 hijacks the cells, who is at risk of getting infected.

Everyone is at risk, however, hypertensive and diabetic patients could be at high risk because of the increase expression of ACE2 in such individuals.

As the saying always goes, “Prevention is better than cure.” Let us protect ourselves from getting infected. CORONAVIRUS is real. Be on guard.

Ways we can protect ourselves from getting infected with the virus include but not limited to;

1. Regular handwashing with soap and water for at least 20 seconds OR hand rubbing with alcohol-based sanitizers that contain at least 60%
2. Practice common cough or sneezing etiquette such as covering of mouth with handkerchief or tissue paper when coughing or sneezing OR wearing of face
3. Keep distance of at least one meter away from the person(s) showing signs of fever, dry cough and difficulty in
4. If contact with a sick person or potentially infected surfaces or objects occur, those involved must not touch their eyes, nose or mouth with unwashed
5. Seek treatment immediately if the infection is suspected or if symptoms occur or when advised by a health
6. Contact any of the national emergency numbers immediately if the infection is suspected or if symptoms

0552222004, 0552222005, 0509497700 and 0558439868

Finally, I urge you to join the campaign on the pandemic COVID-19 sensitization in order to increase awareness. Tell a friend to tell a friend, CORONAVIRUS is real.

EMMANUEL NII OTOO DODOO
A FIFTH YEAR DOCTOR OF MEDICAL LABORATORY SCIENCE STUDENT UNIVERSITY FOR DEVELOPMENT STUDIES (UDS), TAMALE CAMPUS.

0246877170, dr.otoo1@gmail.com