COVID-19

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Structure:

• Large (60-140 nm diameter)
• Spike-like projections (4-12 nm) on surface
  • Proteins spikes
• Genome of single stranded RNA
  • Encoding structural and non-structural proteins
• Surrounded by membrane made of lipids and proteins (envelope)

Replication

1. Virus enters body mainly through mouth or nose
2. Protein spikes on surface of envelope attach to specific proteins on the surface of a cell
3. The virus’s membrane fuses with the cell’s membrane, releasing the virus’s RNA genome into the cell
4. The cell’s ribosomes translate the RNA into proteins, including viral RNA polymerase 
5. The RNA polymerase transcribes the virus’s RNA, making more RNA copies that are translated into proteins
6. Also makes more copies of the virus’s whole genome
7. New viral genome and proteins combine to form a new virus that is packaged into a new envelope formed from the cell’s membranes
8. Newly formed viruses travel to the cell’s surface and are released outside the cell
9. The new viruses can infect other cells, or leave the body in mucus and saliva droplets
10. Can infect others even if asymptomatic

Mutation

• Single RNA genome has genes that can encode proteins
• The arrangements of nucleotides in the genomes determine which proteins it codes, e.g. UAG, AGG, etc

1. The virus makes strands of complementary RNA called template RNA
2. Template RNA is used to produce copies that match their original virus’s genome
3. This genome replication process is prone to errors, also known as mutations
4. Mutations can occur at random anywhere in the genome, e.g. Adesine is replaced with Guanine
   • Nucleotides substituted for another nucleotide, added in the wrong place, or left out
5. When the mutated virus infects another cell, all the new viruses will have this same mutation, plus any new mutations that have occurred
   • This may affect a virus’s ability to spread in a population

Zoonotic Diseases

• Infectious disease that is transmitted from animals to humans, or vice versa

Is COVID-19 a Zoonotic Disease?

• COVID-19 has been classified by the World Health Organisation (WHO) as a zoonotic disease
• However, no animal reservoir has been found
• Proposed as an “emerging infectious disease(EID) of probably animal origin”
• Sars-CoV-2 has been detected in multiple species of animals, including cats, dogs and furrets
• The initial COVID-19 patients were presumably exposed at a seafood market
• Even though it spreads from human to human, it was likely transmitted from an animal first
• Therefore, it’s zoonotic