Food Microbiology &
Helen Billman-Jacobe &
Food-borne viral diseases
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Ray and Bhunia Ch 2, 24, 28, 29
Intended learning outcomes
• Describe the characteristics of viruses that enable them to be transmitted in food and/or water
• Describe how some viruses can persist in food commodities
‘Small infectious agent that replicates only inside living cells of an organism.’
Viruses infect all types of life forms
Very basic structure:
Genome (DNA or RNA, ss or ds, linear, segmented, +ve or –ve sense) Protein coat (capsid)
Enveloped or unenveloped
Lipid bilayer (cell membrane) Glycoproteins (different functions) Sensitive to desiccation, heat, detergents Limited survival outside the host.
Most common food-borne viruses
• Norovirus (Caliciviridae) – non-enveloped, ssRNA
• Hepatitis A virus (Picornaviridae) – non-enveloped, ssRNA
• Hepatitis E virus (Hepeviridae) – non-enveloped, ssRNA
• Human rotavirus (Reoviridae) – non-enveloped, segmented RNA
• Other viruses (Adenovirus, Astrovirus, Sapovirus, Enterovirus, Parvovirus, Aichi virus)
• Emerging viruses (Nipahvirus, SARS-Coronavirus, Flavivirus[TBE], Avian influenza virus H5N1)
Clinical syndromes
Gastroenteritis (diarrhoea, vomiting)
Norovirus, human Rotavirus (Adenovirus, Astrovirus, Sapovirus)
Enterically transmitted hepatitis
Hepatitis A and E
Viruses and food
Viruses do not replicate in food
Viruses do not cause deterioration of food Viruses are hardy and persist in the environment
Food hygiene guidelines which are optimised for controlling bacteria are not always effective against viruses
Transmission
Faecal-oral route
Person-to-person (NoV and HAV) – secondary spread Contaminated water, food, infected food handler Very low infectious dose (1-100 virions)
Very high levels of viral shedding in infected individuals (107 virions per gram of stools)
Transmission
Human sewage and faeces
• Contamination of bivalve molluscs
• Pre-harvest contamination of fresh-produce
(irrigation, washing, fertiliser)
• Potential for contamination with multiple viruses
• Conducive to viral evolution and emergence of new virus strains
• Recombination (NoV) or reassortment (HRV)
Jocobsen and Wiersma (2010). Vaccine 28: 6653-7
Transmission
Infected food handlers
• >107 viral particles per gram of faeces
• Viral shedding as early as 12hr after exposure (before
clinical symptoms)
• Shedding for several weeks (after recovery)
• Asymptomatic infections and shedding (5.2-19% NoV; Netherlands)
• Direct contamination of food or equipment
• At any stage of the farm-to-fork chain
• Vomitus – widespread contamination
Transmission
Zoonotic transmission
Animal faeces
HEV in pig faeces SARS-coronavirus Nipah in fruit
HEV in liver and meat of deer or wild boar HEV in pig meat and organs
Epidemiology
Susceptibility varies depending on aetiological agent:
• NoV – all ages
• HAV – asymptomatic in children
• HRV – in children and infants
• HEV – severe in pregnant women
Determining incidence is difficult (person-to person transmission)
Control measures different to those used for bacterial food-borne pathogens
Priority virus-commodity combinations
1. NoV and HAV – Bivalve molluscan shellfish (oysters, clams, cockles and mussels)
• Faecal contamination of harvesting areas
• Persistence for 8-10 weeks in contaminated
live shellfish
• Molluscs can actively accumulate and concentrate viruses
• Light cooking does not completely inactivate the viruses
Priority virus-commodity combinations
2. NoV and HAV – Fresh produce
• Sewage-contaminated water
• Infected food handler
• Pre-or post-harvest
• 20M Ha agricultural land irrigated with raw, treated or partially diluted wastewater
• Global market
Priority virus-commodity combinations
NoV and HAV – Prepared foods
Infected food handlers
Poor personal hygiene
Outbreaks with hundreds of cases
Foods that do not receive terminal heating before consumption
Deli, bakery, salads, ready to eat foods
HRV – water for food preparation
Emerging viruses and associated commodities
Risk assessment for NoV and HAV
Bouwknegtet al (2015). Quantitative farm-to-fork risk assessment model for norovirus and hepatitis A virus in European leafy green vegetable and berry fruit supply chains. Int J Food Micro 198: 50-58.
Detection of the aetiological agents
Foodborne viruses cannot readily be enriched by culture methods
Molecular methods to detect viral nucleic acid
• Low numbers of organisms – sampling and testing large volumes of food
• Need to extract and concentrate viruses prior to detection
• Need for extracts to be free of inhibitors of detection methods
• Does not indicate presence of viable virus
Large variety and complexity of foods
• Food handler or irrigation water – surface contamination
• Bivalve molluscs – internal
High degree of genetic variability Complex task and costly
Model organisms – limitations!
Considerations for control
Persistence of foodborne viruses
HRV – 9 days at 20oC
Low humidity favours Adenovirus (35 days), HAV and HRV High humidity favours for Enterovirus
Weeks or months in shellfish
Longer than shelf-life in fresh produce
Considerations for control
Stability during processing
Survive prolonged periods at low (3-4) or high (9-10) pH Variable depending on process and substrate
Standard milk pasteurisation – inactivate HAV
Much longer process to inactivate HAV in bivalve molluscs Resistant to ionising radiation
Refrigeration and freezing normally help preserve viruses
CONTROL MUST FOCUS ON PREVENTION OF CONTAMINATION
Decontamination of hands
Hand washing, streaming water and towel drying
Hand sanitisers not as effective (only 1-2 log10 reduction)
Decontamination of surfaces
Viruses easily transferred from hands to surfaces, and vice-versa Common chemical disinfectants do not effectively inactivate HAV
Difficult to know if measures were effective
Control by prevention
For molluscs and fresh produce – no realistic post-harvest risk management measures (except cooking)
Bivalve molluscs
Growing areas versus sewage
Collaboration (public health authorities, food safety authorities, wastewater treatment authorities, producers)
Monitoring virus occurrence in production areas – appropriate analytical methods Depuration is not effective
Batch testing of food not recommended
No aquaculture operations in areas susceptible to sewage contamination
Control by prevention
Fresh produce
Good quality water for irrigation, fertilisation, harvest and packing Water quality guidelines
Adequate sanitary facilities available
Personal hygiene of manual harvesters
Management of ill employees and return to work guidelines Personal hygiene – hand washing
Education of handlers and supervisors
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