ABOUT COVID

22.12.2020

Let's have an introductory overview of what we for now know about this illness and its genetics.

The pulmonary system:

The human pulmonary system is vulnerable to infections due to contact-based inoculation of infectious material in droplets through the eyes, nose, or mouth, and airborne transmission is effective as seen e.g. in the plethora of viral respiratory diseases affecting individuals of all age groups.

Thus, respiratory viruses pose a continuous pandemic threat, of which coronaviruses and specifically the genus Betacoronavirus in the family Coronaviridae is a subset.

Despite recent efforts in basic and translational influenza and coronavirus research, there is still no vaccine against coronaviruses for use in humans (this includes SARS and MERS).

Risk factors: 

- Hypertension

- Diabetes

- Lung

- Pathologies

- Heart disease

- Advanced age with a picture of previous associated pathologies

- Inmunosuppressed people.


GENERAL INTRODUCTION :

  • Origins of the virus: 

Coronaviruses (CoVs) are a large family of viruses, called Coronaviridae. Most cases cause respiratory diseases as the target receptors of the virus are on the lungs cells.

CoVs can infect several animal species as well, for example, SARS-CoV infected civet cats and infected humans in 2002, and MERS-CoV is found in dromedary camels and infected humans in 2012.

A virus that is regularly transmitted from an animal to a human is called a zoonotic virus. One of the tasks is to know which is the zoonotic origin to prevent more contagions in the future, as the zoonotic source of SARS-Cov-2 is currently unknown. The first human cases of COVID-19, the coronavirus disease caused by SARS-CoV-2, were first reported from Wuhan City, China, in December 2019.

When a virus passes from animals to humans for the first time it is called a spillover event.

  • Similar viruses: 

CoVs belong to the family Coronaviridae, which comprises a group of enveloped, positive-sensed, single-stranded RNA viruses 1,2. These viruses harboring the largest genome of 26 to 32 kilobases amongst RNA viruses were termed "CoVs" because of their crown-like morphology under electron microscope 2,3.

Structurally, CoVs have non-segmented genomes that share a similar organization.

Approximately two-thirds of the genome contains two large overlapping open reading frames (ORF1a and ORF1b), which are translated into the pp1a and pp1ab replicase polyproteins.

  • Genetics: 

CoVs are divided into four genera: alpha-, beta-, gamma- and delta-CoV

All CoVs is currently known to cause disease in humans to belong to the alpha- or the beta-CoV .

Coronaviruses are enveloped, positive-stranded RNA viruses of mammals and birds. These viruses have a high mutation rate and gene recombination rates, making them ideal for pathogen evolution.

The genetic material of a virus is either RNA or DNA. A virus that has RNA as its genetic material is called an RNA virus, while that having DNA as its genetic material and replicates using a DNA- dependent DNA polymerase is termed a DNA virus.

The polyproteins are further processed to generate 16 non-structural proteins, designated nsp1~16. The remaining portion of the genome contains ORFs for the structural proteins, including spike (S), envelope (E), membrane (M), and nucleoprotein (N). Several lineage-specific accessory proteins are also encoded by different lineages of CoVs .

Emerging and re-emerging viral diseases have recently attracted worldwide attention. Ebola, zika, H5N1 avian influenza, severe acute respiratory syndrome (SARS), and many other emerging viral diseases have proved fatal and caused worldwide concern.

Common attributes of emerging viral diseases include unpredictability, high morbidity, and potential for the rapid spread of diseases which may lead to substantial social impacts. The recent Ebola crisis and the outbreak of Zika virus have indicated that the world is unprepared to address emerging viral diseases. 

  • Infections: At this stage, it is not possible to determine precisely how humans in China were initially infected with SARS-CoV-2.

However, all available evidence suggests that SARS-CoV-2 has a natural animal origin and is not a manipulated or constructed virus. SARS-CoV-2 virus most probably has its ecological reservoir in bats. SARS-CoV, the virus that caused the SARS outbreak in 2003 and probably also had its ecological reservoir in bats, jumped from an animal reservoir (civet cats, a farmed wild animal) to humans and then spread between humans. Similarly, it is thought that SARS-CoV-2 jumped the species barrier and initially infected humans from another animal host.

Since there is usually very limited close contact between humans and bats, it is more likely that transmission of SARS-CoV-2 to humans happened through an intermediate host, that is another animal species more likely to be handled by humans. This intermediate animal host could be a domestic animal, a wild animal, or a domesticated wild animal and, as of yet, has not been identified.