Paul McMenemy – pmc@maths.stir.ac.uk

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 – pmc@maths.stir.ac.uk 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 – pmc@maths.stir.ac.uk 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

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

- Fever- Headache- Body aches

Paul McMenemy – pmc@maths.stir.ac.uk 4

Reduce NoV in oysters: Reduce NoV outbreaks

Norovirus in Shellfish Industry

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

Paul McMenemy – pmc@maths.stir.ac.uk 5

U.K. Oyster Supply Chain

Harvest

Wholesale

Imports

Retail

Consumer

Depuration

Initial focus of study

Paul McMenemy – pmc@maths.stir.ac.uk 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 – pmc@maths.stir.ac.uk 7

Probability Distribution Model – Depuration Stage

• Use existing pre-depuration data (courtesy - james.lowther@cefas.co.uk) – Existing data split for genome types I and II– Find NoV count per oyster distribution function

Paul McMenemy – pmc@maths.stir.ac.uk 8

Probability Distribution Model – Depuration Stage

• Lognormal probability density function is:

,

• Function to show relationship between and , ( – rate of change variable):

• As , we can generate a p.d.f. for from:

Paul McMenemy – pmc@maths.stir.ac.uk 9

Probability Density Function for

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

Paul McMenemy – pmc@maths.stir.ac.uk 10

plots for to

Paul McMenemy – pmc@maths.stir.ac.uk 11

Uses of Model

• Used to predict level of NoV present after time 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 – pmc@maths.stir.ac.uk 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 – pmc@maths.stir.ac.uk 13

Thank you for listening…Impact Collaborative Studentship funded by:

The University of Stirling

and

Centre for Environment, Fisheries & Aquaculture Science