41. Viral Disease Outbreak

Question 1

Overview of coronavirus

Answer 1

• recongised in a range of animal species, widespread among mammals and birds
• can cross species barriers to infect new animal species
• has 4 groups - alpha, beta, gamma, delta - based on antigenic relationships of spike, membrane and nucleocapsid proteins
• has a proof reading mechanism to reduce mutation

Question 2

Morphology and structure of coronavirus

Answer 2

• pleomorphic and enveloped
• club-shaped surface projections - trimers of spike protein - classic crown appearance (distinctive arrangement of spikes from surfaces)
• non-segmented single-stranded RNA genome of around 30kb - largest known RNA virus
• helical nucleocapsid

Question 3

Replication of coronavirus

Answer 3

• attach to receptors on host cells via S protein
• tissue tropism mainly determined by the S1 part of S protein and by the type and distribution of receptors on host cells
• viruses replicate in host cell cytoplasm with a growth cycle of 10-12 hrs

Question 4

Types of coronavirus and immunity in humans

Answer 4

• four seasonal human coronaviruses - common cold
• immunity to this is short

Question 5

Transmission of human covid

Answer 5

• respiratory droplets
• direct or indirect contact

Question 6

Virus genetics of covid-2

Answer 6

• enveloped single-stranded RNA virus
• beta-coronovirus
• 79% nucelotide similar to SARS virus
• 96.2% same to bat covid RaTG13
• most closely related to virus from horseshoe bat

Question 7

SARS 2003 overview

Answer 7

• severe acute respiratory syndrome
• first occurred in china 2002
• SARS-CoV animal virus in origin, natural reservoir (crossed species barrier to humans)
• transmission in droplets, direct/indirect contact, excreted in faeces, on smooth surfaces
• spectrum of illness of severe respiratory disease to milder presentations - fever
• inflammatory damage - increased levels of proinflammatory cytokines associated with pulmonary inflammation and severe lung damage

Question 8

Impacts of SARS

Answer 8

• social and economic disruption
• impact on travel internationally
• impact on health services

Question 9

Explain MERS 2012

Answer 9

• middle eastern respiratory syndrome
• reported in saudi arabia - spread to other countries
• MERS-CoV, a coronavirus
• MERS-CoV endemic in dromedary camels and causes outbreaks of zoonotic origin in Arabian peninsula

Question 10

What is MERS like?

Answer 10

• 2-14 day incubation
• severe acute respiratory illness - fever, cough, shortness of breath
• more severe in older, weakened immune system, chronic disease like cancer, renal disease, diabetes
• transmission from infected patient secretions, close contact

Question 11

Mutation rate of SARS-CoV2

Answer 11

• relatively low - around 2.5 mutations per genome per month
• similar to other covids
• ongoing genome sequencing is critical to understadning diversity of virus and vaccine development

Question 12

Virus structure of SARS-CoV-2

Answer 12

• viral envelope coated by spike glycoprotein, envelope and membrane proteins
• host cell binding and entry mediated by spike proteins

Question 13

Viral entry and interaction of SARS-CoV-2 in humans

Answer 13

• enters human host cell by binding to human angiotensin-converting enzyme 2 (ACE2) receptor with viral spike protein
• distribution of ACE2 receptors explains sites of infections and symptoms
• receptors found on epithelium of other organs like intestine/endothelial cells in kidney and blood vessels
• higher infectivity and rates or transmission than related viruses like SARS and MERS

Question 14

How infectious is SARS-CoV-2?

Answer 14

• highly
• R0 to be around 2.5 to 3.51 which is higher than SARS/MERS

Question 15

What is the basic reproduction number?

Answer 15

• R0
• average number of secondary infections produced by typical case of infection in a population where everyone is susceptible
• used to measure transmission potential

Question 16

Why is SARS-CoV-2 so infectious?

Answer 16

• infects upper respiratory tract as oppose to lower tract in SARS/MERS
• viral particles have less distance to travel in airway to reach target cells (easy transmission)
• also structural differences in surface proteins and viral load kinetics of SARS-CoV-2

Question 17

Route of transmission for SARS-CoV-2

Answer 17

• infected respiratory droplets
• aerosols
• direct/indirect contact with nasal, conjunctival, oral mucosa
• respiratory particles inhaled or deposited on mucus membranes
• fomites
• still viable on smooth surfaces at lower temp and humidity for many days like air-conditioned stainless steel

Question 18

Both SARS 1 and 2 are readily inactivated by …

Answer 18

commonly used disinfectants

Question 19

Duration of infection of SARS-CoV-2

Answer 19

• peak load is observed at time of symptom onset or in first week of illness
• highest infectiousness potential just before or in first 5 days of symptoms

Question 20

Disease severity of SARS-CoV-2

Answer 20

• rages from asymptomatic to lethal
• dysregulated immune responses can contribute to severe disease
• excessive immune response to SARS-CoV-2 reported, high levels of cytokine release and ‘cytokine storm’

Question 21

Systemic impact of SARS-CoV-2

Answer 21

• in severe cases, triggers aberrant host immune response
• overproduction of pro-inflammatory cytokines
• cytokine storm
• acute respiraotry distress syndrome
• septic shock/multi-organ dysfunction

Question 22

It is suggested that SARS-CoV-2 isn’t limited to airway cells but …
Explain

Answer 22

• cardiac, gut and immune cells can be targeted too
• secondary results on inflammation and blood clotting suspectedly
• affect multiple organ systems in body
• chronic symptoms caused like long lasting fatigue, shortness of breath

Question 23

SARS-CoV-2 has 2 types of variant. Name them

Answer 23

• variant of interest
• variant of concern

Question 24

Explain SARS-CoV-2 variant of interest

Answer 24

• has mutations that are suspected or known to cause significant changes and circulating widely

Question 25

Explain SARS-CoV-2 variant of concern

Answer 25

• known to spread easily, cause more severe disease, escape body’s immune response and change clinical presentation

Question 26

Explain SARS-CoV-2 Omicron variant

Answer 26

• most heavily mutated variant to emerge so far and carry those similar to previous variants of concern
• associated with enhanced transmissibility and partial resistance to vaccine induced immunity
• unusually large number of genetic changes - particularly in spike protein