FOOD-BORNE DISEASES

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Introduction

• Causes of food-borne diseases/illnesses:

1. Chemical toxins (‘residues’)2. Biotoxins – endotoxins & exotoxins3. Infectious agents – exogenous &

endogenous (‘zoonoses’)

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Introduction contd

endotoxins & exotoxins

lipopolysaccharide (LPS) : protein

part of bacterium : extracellularno toxoid : toxoid

low potency : high potencylow specificity : high specificity

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Mode of action of some bacterial toxins

S. aureus – A(alpha-toxin)

E. coli – B(shiga toxin)

C. botulinum – C(exo-enzyme)

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Introduction contd

• Food hygiene vs food safety food hygiene – microbiological safety of food food safety – abscence of

chemicals/residues

• Not necessary to have ‘sterile’ food

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Prevention of food-borne diseases

• Organisms - characteristics

1. where from2. types & strains3. behaviour in food4. survive or are killed by

measures to inactivate

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Prevention of food-borne diseases, contd

• Food – characteristics

Water activity (aw), pH and temperature

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What influences occurrence of food-borne

diseases/illnesses?

• Food source• Food storage• Food preparation• Food handlers

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What influences occurrence of food-borne

diseases/illnesses?

• Time-temperature abuse• Infected food handlers or

inadequate hygiene during handling of food

• Consumption/use of unsafe food sources

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Types of illnesses/diseases

• Upper GIT – nausea & vomiting

• Lower GIT – cramps & diarrhoea

• Neurological signs

• General symptoms

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Types of illnesses/diseases

Upper GIT signsNausea, retching, vomiting, abdominal

pain, diarrhoea & prostration

• S. aureus and its toxins• B. cereus and its toxin

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Types of illnesses/diseases

Lower GIT signsLower abdominal cramps & diarrhoea

• Clostridium perfringens, Bacillus cereus

• Salmonella, Shigella, ET E. coli, Yersinia enterocolitica, Campylobacter jejuni, Vibrio cholera

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Types of illnesses/diseases

Lower GIT signs, continuedLower abdominal cramps & diarrhoea

• Giardia intestinalis• Cryptosporidium parvum

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Types of illnesses/diseases

Neurological signsVisual disturbances, vertigo, tingling

sensation & paralysis

• Clostridium botulinum

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Types of illnesses/diseases

General symptomsFever, chills, malaise, prostration, aches,

swollen lymph nodes

• S. typhi, L. monocytogenes, C. jejuni• Hepatitis A

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Risks of contracting food-borne disease depend on:

• Host susceptibilityAge

General health

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Infective dose

• Frequently exptrapolated• Feeding studies (healthy, young

adult volunteers)

• Estimates (data from outbreaks)

• ‘Worst case’ estimates

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Risk assessment – variable infective doses

• Interaction – food substrate & environment

• pH susceptibility • Type and strain

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Control of food contamination

• Micro-organisms in food & water

shellfish fruits & nuts

beanswatermelons

spices & herbsvegetables

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Control of food contamination

• Infection of animals – milk, eggs or meat

• Contaminated skins and guts - slaughter & dressing

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Pathogenic Bacteria

• C. botulinum, C. perfringens - Soil, hide, faecal material

• Staphylococcus aureus toxin - Human (nostrils and hands)

• Listeria monocytogenes- Soil, hide, faecal material

• Campylobacter spp. - GIT (esp. poultry)

• E. coli O157:H7 - GIT

• Salmonella spp. - GIT / Hide

• Yersinia enterocolitica - GIT

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Control of food contamination

• Ideal = growing & harvesting stages• But – ‘world is not sterile’• Prevent, reduce or limit by:

Not allowing products from clinically ill animals to enter food chain

Classical meat inspection - grossHACCP - microscopic

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The chain of production from ‘farm to fork’ of food from animals

Production

Processing

Final preparationand cooking

Farm, Feedlot, Fishing siteSlaughter Plant, Cannery,Packer, Food Factory

Final Kitchen: commercial, institutional or domestic

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The chain of production from farm to fork -

prevention can occur at each step

Production

Processing

Final preparation and cooking

Feed, water, manure treatment,biosecurity, probiotics, vaccinesHACCP, slaughter hygiene,pathogen reduction andelimination (pasteurization, irradiation)

Cooking, preventingcross-contamination,worker education and hand washing

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Prevention of Food Poisoning

WHO ‘ten golden rules’

• Food processed for safety• Thoroughly cook• Eat immediately• Store carefully• Reheat thoroughly

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Prevention of Food Poisoning

WHO ‘ten golden rules’ contd

• No contact between raw & cooked• Wash hands• Keep food preparation surfaces

clean• Protect from pests• Use potable water

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Food-borne disease outbreaks & food spoilage

• Contamination with undesirable micro-organisms

• Unacceptable levels of micro-organisms

• Treatment did not result in inactivation

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Food-borne disease outbreaks & food spoilage

• Preventing/limiting contamination

• Preventing/limiting spread• Preventing growth• Preventing survival of organisms

& persistence of metabolites

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Microbiological/chemical hazards

• Micro-organisms – part of nature Chemicals – many are man-made• Micro-organisms change numbers• Uneven distribution in food• Clinical symptoms – acute• Variable consumer susceptibility