Respiratory Pathogens, Influenza and Corona Viruses Flashcards
1
Q
How does airborne transmission occur (aerosols)
A
- Give rise to large (ground / surfaces) and moderate to small (micro droplets in air) droplets
- Effectively transmitted only over short distances
- Sneezing and coughing
2
Q
Describe streptococcus pyogenes disease
A
- Group A streptococci
- Upper respiratory tract of healthy individuals, can cause pus-forming wounds
- Causative agent of strep throat
- Strains carry lysogenic bacteriophage (exotoxins causing TSS / scarlet fever)
- Untreated can lead to rheumatic fever
3
Q
What is acute rheumatic fever
A
- Caused by mimicry between M protein / host tissue of streptococcus pyogenes
- Major issues for indigenous
- Long term prophylactic antibiotic regime (poor compliance)
- No vaccine
4
Q
What is diphtheria
A
- Severe respiratory disease
- Caused by Corynebacterium diphtheriae (irregular rods during growth)
- Preventable and treatable (resistance via previous infection / immunisation)
- Spreads via airborne droplets
- Pathogenic strains lysogenised by bacteriophage β, produce exotoxin causing tissue death (prevent protein synthesis in throat)
5
Q
What is pertusis
A
- Whooping cough
- Infectious respiratory disease
- Caused by Bordetella pertusis
- Observed in school age children
- High risk are those inadequately immunised
- Consistent and upwards trend of infection since 1980’s
6
Q
Generally describe respiratory viral infections
A
- Less easily controlled by chemotherapeutic methods
- Most prevalent human infections
- Most viral diseases are acute, self-limiting infections
- Few serious diseased have been effectively controlled by vaccines (small pox / rabies)
7
Q
What is measles
A
- Caused by paramyxovirus
- Acute, highly infectious, often epidemic
- -ve strang RNA virus
- Virus enters nose / throat via airborne transmission
- Isolated outbreaks due to worldwide immunisation program (1960’s)
- Still over 600,000 deaths per year worldwide
- Decline in vaccination causes global spread
8
Q
What is mumps
A
- Caused by paramyxovirus
- -ve strand RNA enveloped virus
- Highly infectious, occasional outbreaks
- Airborne droplets / saliva
- ## Inflammation of salivary glands
9
Q
What is rubella
A
- +ve strand RNA enveloped virus of toga group
- Symptoms resemble measles
- Milder and less contagious
- Routine childhood immunisation
10
Q
What is varicella-zoster
A
- Papular rash (chicken pox)
- dsRNA enveloped varicella-zoster virus
- Transmitted by infectious droplets
- Lifelong latent infection in nerve cells
- Virus occasionally migrates to kin causing shingles
11
Q
What is the common cold
A
- Caused by rhinoviruses
- ssRNA +ve enveloped virus
- Nearly 115 strains identified
- 15% colds due to coronaviruses, 10% due to other viruses
- Antiviral drugs are ineffective
- Large number of pathogens precludes complete protective immunity / vaccines
12
Q
What is influenza
A
- RNA virus orthomyxovirus, enveloped
- Subgroups due to allelic expression of haemagglutinin (HA) and neuraminidase (NA) proteins
- 14kb genome (10 genes)
- 8 ssRNA -ve segments (A/B)
- 7 ssRNA -ve segments (A/C)
13
Q
What is influenza A
A
- Affects wide variety of birds
- Ancestor of influenza strain circulating in swine, horses and humans
- 3 polymerase proteins (PB1-3)
- 2 major surface glycoproteins (HA and NA)
- 3 structural proteins (NP, M1-2)
- 2 non-structural proteins (NS1-2)
- Some strains contain PB1, encodes protein involved in host apoptosis
- Can undergo adaptations to infect humans (shift)
14
Q
What is influenza B and C
A
- B: Infects humans
- C: Infects humans, haemagglutinin esterase (HE) assumes function of HA / NA
15
Q
What is antigenic shift
A
- Major change in virus antigen due to gene reassortment (not the same as recombination)
- Replacement of HA and or NA alleles
- When 2 virtues infect the same cell, viral gene segments randomly mix giving rise to a new virus
- Avoid immune detection, high rate of infection, significant morbidity / mortality
- Give rise to pandemic
- Pigs act as mixing vessel for bid and human influenza virus (can then reinfect humans)
16
Q
What is antigenic drift
A
- Minor changes in virus antigens due to gene mutation
- Small changes to the HA and NA proteins
- Caused by plasticity of virus genome (influenza)
- RNA polymerases of RNA viruses lack a proof reading mechanism, mutations accumulate
- Leads to annual outbreaks and limited vaccine efficacy
17
Q
What are characteristics of human influenza and epidemics / pandemics
A
- Occur periodically
- Epidemic when incidence of influenza rises above the seasonal baseline
- Winter outbreaks occur in north / south hemispheres
- 1 type / subtype of influenza can circulate during an influenza season
18
Q
Who is at high risk for influenza
A
- Young children and infants
- Immunocompromised individuals
- Elderly / ageing population
- Un-immunised people
19
Q
What is host specificity in relation to Influenza A (birds vs humans)
A
- Preferential binding of avian viruses to sialic acid receptors, have galactose linked via a2,3-glycosidic bonds
- Molecules are found on intestinal epithelia in birds
- Human sialic acid receptors have a2,6 linked glycosidic bonds
- Limits spread of bird viruses to humans
- Highlights importance of adhesion / specific receptors to allow infection
20
Q
What is genetic reassortment
A
- Reassortment of viral RNA segments
- Expression of new surface proteins (HA or NA)
- Immune system has no existing immunity to Ag
- Random association of 8 different genetic segments in pigs
- If new virus can replicate / transmit from pig to other hosts, pandemic may spread
21
Q
What molecular technique did scientists use to study virulence and pathogenicity of 1918 Spanish flu
A
- Reverse genetics
- Non-pathogenic human viruses showed enhanced virulence when carrying 1918 HA protein
- Recombinant viruses containing 1918 HA / NA proteins were highly lethal in mice
- NS1 protein affects virulence by blocking interferon response
22
Q
What are the innate immune mechanisms important for control of influenza virus
A
- Release of type 1 IFNs
- Produce Abs to recognise HA / NA
- Abs block viral binding to target cells / subsequent cell entry
- Abs not essential for protection (prevent reinfection)
- Increased memory leads to decreased viral load
- Importance of having an effective vaccine
23
Q
How do pigs aid transmission from birds to animals (influenza)
A
- Due to host receptor specificity, direct transmission of bird flu viruses to humans is uncommon
- Pigs express both types of sialic acid receptors
- Pigs can be infected by human and bird flu
- Allows mixing vessel where genetic reassortment and selection of novel viruses may occur
- Last swine flu virus caused pandemic in 2009
24
Q
What are the clinical symptoms / complications of influenza
A
Symptoms
- Fever and chills, sore throat, headache, retro-orbital pain
- Severe myalgia (muscle aches), fatigue, prostration, and general malaise
- Nausea, vomiting and diarrhoea
Complications:
- Infection with bacteria, especially, Staph. aureus, Haemophilus influenzae, Strep. pneumoniae or Strep. pyogenes resulting in pneumonia
- Encephalitis with confusion, delirium and coma may occur as well as myocarditis
25
Q
What was the Spanish flu of 1918
A
- H1N1 influenza A
- 50 million deaths worldwide
- Low transmissibility but high per-case mortality rate
- High death rate for young adults (14-34)
- Wide dissemination, high and rapid replication
- Aberrant and persistent activation of cytokines
- 2.5% case fatality
