Slide 1

Norovirus – A Case Study

1st Year PhD Student – Paul McMenemy(UoS)
Primary Supervisor – Dr Adam Kleczkowski (UoS)
Secondary Supervisor – Dr Frans de Vries (UoS)
Industrial Supervisor – Dr Nick Taylor (CEFAS)

Paul McMenemy – [email protected]


Slide 2

News Headlines - Norovirus
• “Cases of the winter vomiting bug 'top a million‘ “ – BBC , 28th Dec 2012
• “New strain of norovirus spreads around the world” – Yahoo News, 9th
Jan 2013

• “New strain of norovirus” – Centre for Disease Control – USA, 14th Jan 2013
• “New Mutant Norovirus Strain to Wreak Havoc on Cruise Industry?”
– cruiselawnews.com, 16th Jan 2013
• GII.4 Sydney strain – nicknamed “Down Ch-under”

• Worldwide impact of new and existing virus strains

• Becoming more prevalent in 21st century
Paul McMenemy – [email protected]

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Slide 3

What is Norovirus?
• Small round structured virus (SRSV)
• World’s main cause of gastroenteritis
• Transmitted via the faecal-oral route
– Eat/drink contaminated foodstuffs
– Touch contaminated surfaces then put fingers in your mouth
– Contact with someone who is infected

• Many different strains of norovirus(NoV)
– Person can be infected multiple times

• Symptoms
– Diarrhoea
– Vomiting, Nausea
– Stomach pain

- Fever
- Headache
- Body aches

(Sources – http://www.cdc.gov/norovirus/about/symptoms.html, http://www.cefas.defra.gov.uk )

Paul McMenemy – [email protected]

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Slide 4

Norovirus in Shellfish Industry
• Main cause - sewage
treatment works
• Prevalent in most bivalves
• Cooking shellfish kills NoV
• Oysters eaten raw in U.K.

Reduce NoV in oysters:
Reduce NoV outbreaks
Paul McMenemy – [email protected]

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Slide 5

U.K. Oyster Supply Chain
Harvest

Depuration

Imports

Wholesale

Initial focus
of study
Paul McMenemy – [email protected]

Retail

Consumer

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Slide 6

Depuration Stage
• Oysters are flushed with clean
water
• Reduces bacterial
contaminants (E. coli)
• Limited impact on virus
counts in oysters
• More straightforward to
model than other stages
• Costly to depurate
• Can reduce oyster quality
Paul McMenemy – [email protected]

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Slide 7

Probability Distribution Model –
Depuration Stage
• Use existing pre-depuration data

(courtesy - [email protected])

– Existing data split for genome types I and II
– Find NoV count per oyster distribution function

Paul McMenemy – [email protected]

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Slide 8

Probability Distribution Model –
Depuration Stage
•

Lognormal probability density function is:

𝑃 𝑥0 = 𝜎
•

1
2𝜋𝑥0

exp( − ln( 𝑥0 − 𝜇)2 /2𝜎 2 ), (𝑥 > 0)
0

Function to show relationship between 𝑥0 and 𝑥𝑡 , (𝜆 – rate of change variable):

𝑥𝑡 = 𝑥0 𝑒 −𝜆𝑡
•

As 𝑥0 ~ 𝑥𝑡 , we can generate a p.d.f. for 𝑃(𝑥𝑡 ) from:

𝑃 𝑥𝑡 𝑑𝑥𝑡 = 𝑃 𝑥0 𝑑𝑥0
⇒

𝑃 𝑥𝑡

Paul McMenemy – [email protected]

𝑑𝑥𝑡
= 𝑃(𝑥0)
𝑑𝑥0

−1

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Slide 9

Probability Density Function for 𝑃(𝑥𝑡 )
𝑃 𝑥𝑡 =
𝑥𝑡
𝜎
𝜇
𝜆
𝑡

−(ln 𝑥𝑡 +𝜆𝑡−𝜇)2
1
exp
2𝜎 2
2𝜋𝜎𝑥𝑡

− norovirus count per oyster at time 𝑡
− standard deviation of logged 𝑥0 data
− mean of logged 𝑥0 data
− rate at which norovirus counts per oyster changes
− number of time periods into depuration process

Paul McMenemy – [email protected]

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Slide 10

𝑃(𝑥𝑡 ) plots for 𝑡 = 0 to 𝑡 = 5

Paul McMenemy – [email protected]

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Slide 11

Uses of Model
• Used to predict level of NoV present after
time 𝑡 in depuration
• Used to determine optimal time in depuration
to minimise NoV risk
• Allow cost-benefit analysis of depuration on
NoV mitigation
• Could be also used for modelling E. coli

Paul McMenemy – [email protected]

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Slide 12

Further Work
• Model v Experimental Data :
– Data on NoV count before and after depuration
needed to validate and fine-tune model

• Economic work on cost-benefit analysis
• Create models on other stages of supply chain
– Wholesale/Retail (storage, testing)
– Consumer (awareness, frequency of
consumption)
Paul McMenemy – [email protected]

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Slide 13

Thank you for listening…
Impact Collaborative Studentship funded by:

The University of Stirling

and

Centre for Environment, Fisheries & Aquaculture Science

Paul McMenemy – [email protected]

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