15.3.1.2.1: Coronaviruses
- Page ID
- 42679
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Recommended guide to SARS-CoV2 by Scientific American: https://www.scientificamerican.com/i...e-coronavirus/
Virus
- Genetic material: (+)-strand ssRNA
- Virion structure: helical capsid; enveloped with prominent glycoprotein spikes
- the name "corona" means crown and refers to the resemblance of the virus to a crown due to the prominent glycoprotein spkies
- Glycoprotein adhesin(s) (spikes): simply referred to as spike (S) proteins
Replication (Figure \(\PageIndex{1}\))
- Attach to viral receptors in the respiratory tract
- SARS and SARS-CoV2 (cause of COVID-19) specifically bind to angiotensin-converting enzyme 2 (ACE2) (Figure \(\PageIndex{2}\))
- ACE2 plays a role in regulating blood pressure/vasoconstriction and is found throughout the body, not just in the respiratory tract
- (+)-sense RNA is used directly by infected host cell as mRNA to make viral proteins
- RNA-dependent RNA polymerase (RdRP) is used to make (-)-sense RNA copies of the genome; the (-)-sense RNA can then be used as template to make more (+)-sense RNA genome
- like in other RNA viruses, the use of an RdRP for genome replication results in a high rate of mutation
- mRNA is translated into a long polyprotein which is then cut into active proteins by a protease (similar to HIV) (not shown in figure)
Transmission
- Inhaled in respiratory droplets
- SARS-CoV2 (cause of COVID-19) can also
- be transmitted through aerosols
- enter through the eye
- SARS-CoV2 (cause of COVID-19) can also
- Viruses which cause severe respiratory syndromes (Middle East Respiratory Syndrome (MERS), Sudden Acute Respiratory Syndrome (SARS), and COVID-19) are throught to be of zoonotic origin
- All three have been found in bats
- MERS is also found in camels
Epidemiology
- Most diseases caused by coronaviruses in humans are mild common colds similar to rhinovirus
- second most frequent cause of common cold (10 - 15% of colds)
- For SARS (Sudden Acute Respiratory Syndrome) and COVID-19 the most at risk are
- healthcare workers
- others in close contact with infected individuals
- elderly
- people with underlying conditions such as high blood pressure (related to the receptor ACE2), diabetes, asthma, COPD (chronic obstructive pulmonary disease)
- For MERS, close contact with camels is a large risk factor
- The severe respiratoty syndromes have relatively high mortality rates:
- SARS 10%
- MERS >50%
- COVID-19
- Original strain 1.5 - 3.0% in most countries, but as high as 8.6% (depends on medical facilities and treatments available)
- Current morality rate seems to be decreasing for recent variants (such as omicron) and due to vaccination and developments in treatment
Clinical Disease
- Common cold: typical common cold symptoms
- Common symptoms of the severe respiratory syndromes:
- high fever
- shortness of breath
- difficulty breathing
- malaise
- body aches
- sometimes gastrointestinal symptoms such as diarrhea (about 10-20% of patients)
- Additional COVID-19 symptoms/effects (note: being COVID-19 is a relatively newly described disease, this information reflects what is currently known to the best of my ability)
- dry cough
- loss of taste and smell
- low blood oxygen
- lung damage/scarring
- cardiovascular effects, including blood clots, heart attack, stroke
- The most severe/fatal cases of COVID-19 result from severe inflammation caused by the immune system in a phenomenon called a "cytokine storm".
- Immune system overreacts to the extent that there is extensive, system-wide tissue damage
- "Cytokine storm and cytokine release syndrome are life-threatening systemic inflammatory syndromes involving elevated levels of circulating cytokines and immune-cell hyperactivation." (https://www.nejm.org/doi/full/10.1056/NEJMra2026131)
- Some people who have been infected with COVID-19 become "long haulers"
- Can even occur in people with mild cases
- symptoms linger for months or development of sequelae
- myocarditis
- abnormal heart rhythm
- persistent shortness of breath
- fatigue
- neurological symptoms: dizziness and "brain fog" to seizures and encephalitis
Treatment and Prevention
- COVID-19 prevention:
- vaccination
- mask wearing in public
- limit activities in public places
- maintain distance from people not in your household (>6 feet)
- quarantine/isolation: follow current CDC guidelines
- COVID-19 treatment:
- Drugs:
- Monoclonal antibodies can reduce disease severity
- Remdesivir is a nucleoside analog that can decrease the length of hospitalization
- Paxlovir (nirmatrelvir and ritonavir) is an oral medication which prevents SARS-CoV2 replication by inhibiting the protease which cuts the synthesized polyprotein into active viral proteins. This drug greatly reduces the risk of hospitalization if taken early in the infection.
- Dexamethasone is a steroid that diminishes the immune response. Helpful to reduce dangerous inflammation in severe disease (prevents/reduces cytokine storm).
- Supportive therapy such as supplemental oxygen or ventilators (in the most severe cases)
- Drugs:
- COVID-19 vaccines:
- There are two types of COVID-19 vaccine that have been or are likely to be approved for use in the US:
- mRNA (Pfizer-BioNTech and Moderna): mRNA code for the spike protein contained within a lipid vesicle
- lipid vesicle fuses with cell membrane and releases mRNA into your cells
- your cells use the mRNA to produce the SARS-CoV2 spike protein and trigger an immune reaction to SARS-CoV2
- ~94% effective with two doses a few weeks apart
- viral vector (AstraZeneca)
- harmless virus capable of infecting humans (an adenovirus in the case of AstraZeneca) is engineered to carry the SARS-CoV2 spike protein gene
- infected cells produce the spike protein and trigger an immune response to SARS-CoV2
- mRNA (Pfizer-BioNTech and Moderna): mRNA code for the spike protein contained within a lipid vesicle
- Everyone who can should get vaccinated
- There are two types of COVID-19 vaccine that have been or are likely to be approved for use in the US: