Lecture 18 - Emerging Viral Disease Flashcards
What is an emerging viral disease?
- Newly appeared
OR
- Previously existed, but rapidly increase in incidence or geographical range
What is an emerging viral disease?
- Newly appeared
OR
- Previously existed, but rapidly increase in incidence or geographical range
What are some examples of emerging viral disease?
SARS-CoV
HIV
Ebola
What are some factors that lead to the emergence of new disease?
- Mutation rate of viruses
- Ecological changes
- Human demographics and behaviour
- Air travel
- Technology and industry
- Public health measures
Most emerging viral diseases are…
Zoonoses
What are some examples of zoonoses?
Birds: influenza
Monkeys: HIV
Bats: SARS-CoV
What does SARS stand for?
Severe acute respiratory syndrome
Describe what happened in the SARS epidemic
2003 First cases in China Spread to 32 countries 800 people died $20 billion
What are the symptoms of SARS?
Fever
Cough
Shortness of breath
Chest X ray –> pneumonia
+ + exposure to SARS patient
How was SARS transmitted?
Person - person
What are some examples of emerging viral disease?
SARS-CoV
HIV
Ebola
What are some factors that lead to the emergence of new disease?
- Mutation rate of viruses
- Ecological changes
- Human demographics and behaviour
- Air travel
- Technology and industry
- Public health measures
Most emerging viral diseases are…
Zoonoses
What are some examples of zoonoses?
Birds: influenza
Monkeys: HIV
Bats: SARS-CoV
What does SARS stand for?
Severe acute respiratory syndrome
Describe what happened in the SARS epidemic
2003 First cases in China Spread to 32 countries 800 people died $20 billion
What are the symptoms of SARS?
Fever
Cough
Shortness of breath
Chest X ray –> pneumonia
+ + exposure to SARS patient
How was SARS transmitted?
Person - person
Airbone droplets from sneezing
What was interesting about the spread of SARS?
20% of cases were Health Care workers –> defied normal control measures
Superspreaders: some people spread the virus to a huge number of people
What type of virus is SARS?
Corona virus
What is the natural host of SARS?
What other animal was a host to a similar corona virus?
Bats
Civit cat
Which subtypes of influenza are endemic in man?
Type A:
H1N1
H3N2
Which cells in man are infected by influenza?
How about in birds?
What is the significance of this?
Humans: Cells bearing SA a2-6 Galactose
Birds: cells bearing SA a2-3 Gal
Normally prevents avian viruses from infecting man
What happens when the aviacn virus infects man?
Why?
Pandemic
Because no one has any antibody to the new subtype
How is antigenic shift different from antigenic drift?
Describe antigenic shift
Shift:
• bigger change in a shorter period of time
• two different strains / subtypes coming together
• mixture of surface antigens
What is the cause of a pandemic?
Antigenic shift
This is when there is suddenly a new subtype that can infect man
What were the influenza pandemics seen in the 20th century?
Spanish flu: H1N1
Asian flu: H2N2
Hong Kong flu: H3N2
What happens to the existing subtype when there is a pandemic?
The old subtype is replaced.
eg. H3N? –> H1N1 in Spanish flu
How do new human subtypes come about?
Antigenic shift
Mechanism:
• Reassorment
• direct invasion with avian strain, then mutation
Describe what happened in the Spanish flu pandemic?
25-30% population infected
50 million deaths
15-30 yo mainly affected
During WWI
What were the symptoms of Spanish flu?
Pulmonary oedema
Haemorrhage
Cyanosis (purple lips)
Why was the H1N1 of the Spanish flu so lethal?
Don’t know yet, but sequences are currently being studied by Reverse genetics
What is the subtype of Avian influenza?
H5N1 HPAI (Highly pathogenic avian influenza)
What happens to birds that are infected with H5N1 HPAI?
Infects systemically and rapidly brings death
Does H5N1 infect man?
Yes –> lethal
However, it can not be spread from Human-Human
How can HPAI infect systemically?
The cleavage site on HA has mutated
It can now be cut by an enzyme found all over the body
What is the potential route for an H5N1 pandemic?
- Mutation –> Becomes virulent to poultry
- Infects man directly with low efficiency
- Antigenic drift, so that it affects man with high effiency
PANDEMIC
In 1997, there were 20 cases of Avian flu in man. How was the epidemic halted?
Culling of poultry
What is the fatality rate of avian flu?
How does this compare to seasonal epidemic influenza?
H5N1: 60%
Seasonal epidemic influenza: 0.01%
Which drugs are effective against avian flu?
NA inhibitors
Describe the process of reassortment?
In a ‘mixing vessel’
• Pig cells have surface receptors that allow invasion by both human and avian influenza
• Single cell infected with both strains at once
• reassortment
• New strain:
- human internal proteins
- avian HA and NA
What does reassortment bring about?
Antigenic shift
Describe the origin of the 2009 H1N1 pandemic?
1918 H1N1 in North America
+ Swine viral genes
2009 Pandemic H1N1
Describe the infection caused by 2009 H1N1 Swine flu
Same as seasonal influenza: • fever • cough • muscle pains • malaise • fatigue
NB not systemic
Compare lethality of Swine flu, Avain flu and seasonal influenza
Avian flu is highly lethal
Both Swine flu and seasonal influenza aren’t very lethal, unless the individual is immunosuppressed
Compare replicative ability of seasonal flu and swine flu
Swine flu has a greater ability to replicate in lungs
Younger people are getting viral pneumonia
How is Swine flu treated?
NA inhibitors
Can we make vaccines against H5N1 now for when it becomes a pandemic?
Yes, but they probably wouldn’t be effective due to antigenic drift
How can we treat H5N1 if it becomes a pandemic?
NA inhibitors
However, we won’t be able to produce enough
