Food Borne Intoxications: Intentional or Accidental Food Poisoning?

Food borne intoxications are diseases/infections caused by ingestion of toxic materials found in animals and plants. They are metabolic products of microorganisms that they produce as they multiply.

Intoxication could also arise from consumption of various compounds added to food whether intentional or otherwise. These could include compounds that are generally regarded as safe (GRAS), e.g. food colouring or flavouring agents.

The most common food borne intoxications include:

1. Staphylococcus aureus intoxication

Staph. aureus is both infectious and intoxicating. It is a ubiquitous microorganism that is not easy to eliminate.

Intoxication occurs after consumption of foods containing the exotoxins produced by the bacteria.

Alternatively, one can consume the bacteria in the food and the bacteria will multiply rapidly and cause infection after reaching the GIT.

This bacterium produces toxins A, B, C, and D, which are very potent and heat stable. These toxins are also resistant to proteolytic enzymes.

These bacteria easily contaminate food due to their presence on the skin.

Predisposing factors

  • High levels of contamination by the bacteria
  • Foods at pH of 4.5
  • High temperatures (above 15°C; ideally between 35°C and 45°C).
  • The bacteria are present in the food for a long period enough to multiply and produce toxin. For instance, keeping cream at 24°C for five hours of exposure will allow for toxins to be produced. Mashed potatoes will take six hours to achieve the same results while contaminated fish will take 72 hours to produce the toxins.

Staphylococcus aureus has very poor ability to compete with other microorganisms. They occur in foods that have marked reduction in number of other microorganisms.

This is the reason why foods like cured meat and salted foods that kill other microorganisms give Staph. aureus a head start.

Sources of contamination

Man harbours this microorganism on the skin and mucus membrane.

Commonly affected foods include meat and milk products. The bacteria come from the animal and people who handle the milk and meat.

Staph. aureus also causes mastitis.

Modes of transfer

Bacteria moves from one organism to the food and the food becomes a hazard for all who consume it.

High dosage is necessary for propagation and toxin production.


Incubation period usually takes between one and six hours. Observable symptoms include:

  • Nausea and vomiting
  • Abdominal pain and cramps
  • Diarrhoea
  • In severe cases, blood is present in vomit and stool
  • Other symptoms vary based on individual status and dosage of the bacteria. They may include headache, sweating, and marked prostration.

Fatality rates are very low. Recovery happens between 24 to 72 hours.


Tentative diagnosis is done from the symptoms. To confirm the disease, isolate the bacteria and the toxins.

Control measures

  • Avoid conditions that allow toxin production
  • Ensure hygienic preparation and handling of foods.
  • Freezing meat before cooking

2. Botulism

Botulism is an intoxication that affects both animals and people. It comes from the Latin word Botulus, which means sausage because it is majorly associated with sausages.

The disease is very common in animals and produces very severe intoxication often resulting in outbreaks.

It takes a low profile in people but will have pre-formed toxins when one gets infected.


The toxins are produced by Clostridium botulinum, which is harboured in the GIT. It forms highly resistant spores.

It is both proteolytic and non-proteolytic and it can cause food spoilage or produce toxins in unspoilt food.

The bacteria produce several toxins including A, B, C, D, E, and F. All these toxins will occur in both man and animals in varying severity.

Toxins C and D are very common in animals and cause intoxication in animals.

Conditions for toxin production.

A pH range of between 4.6 and 5.3 or above.

The bacteria have a range of favourable temperatures depending on the food in question. The minimum is usually between 25°C and 37°C.

However, some foods can facilitate toxin production at low temperatures of 10°C while others as high as 50°C. Toxins A and B can be produced and temperatures lower than 10°C.

Food preservation method will affect toxin production. Anything that will cause an anaerobic condition will lead to toxin production.

Sources of contamination in animals

Anything rich in organic matter (e.g. cadavers of animals that had these bacteria. Animals tend to eat these when they have pica).

Decaying plant matter may contain bacteria from dead rodents that come into contact with them. When these come into contact with animal feed, they transfer the contamination.

Sources of contamination in man

Animal proteins especially if kept improperly leading to formation of food pH of between 4.6 and 5.3. When this food is consumed after warming slightly, it leads to poisoning.

People who love to eat raw animal products are at a higher risk. Type B poisoning is common in marine foods and fresh water fish.

Highly acidic/spiced/fermented foods or foods with low protein needs delicate handling. Such food may already be spoilt but you will fail to notice it due to the food’s acidic nature. This often leads to outbreaks.

Major sources of these toxins

Toxin type A – is very common in man. It is transmitted through chicken meat, fish, and canned vegetables.

Toxin type B – will occur in both man and horses. It is associated with meat in men and forage/silage in horses.

Toxins types A and C will occur in birds that eat rotten vegetables.

Toxins C and B are common in most domestic animals. They pick the toxin from decaying organic matter.

Type B is common in cattle. They get the toxin from eating contaminated feed.

Toxin type E is usually associated with man and wild birds. They contact it from marine foods and fish.

Type F usually affects man. Common in Europe.

Symptoms of intoxication in man

The toxins interfere with the production of acetylcholine leading to motor paralysis.

Incubation period is between 12 and 36 hours. It can be shorter (4 hours) or longer (36 hours) depending on the individual.

Observable symptoms include:

  • Upset of the gastrointestinal tract
  • Nausea
  • Vomiting
  • Burning sensation
  • Diarrhoea with/without pain
  • Constipation may occur in some cases.

Nervous symptoms will set in as follows:

  1. Dizziness followed by drying up of the mouth
  2. Pain in the pharyngeal region
  3. Blurred vision due to paralysis of the optical region
  4. Mydriasis – normal dilation, jerky or involuntary
  5. Nystagmus – when the eyes fixate on an object/target
  6. Loss of light stimuli, which will lead to blindness
  7. Temperature is usually unaffected and people will not lose memory.
  8. When the muscles are affected, swallowing food will be very difficult
  9. Pharyngeal muscles will be affected leading to respiratory failure and even death

In animals, the effects vary in severity. Mostly affected are chicken and cattle.

  1. It will lead to sudden deaths
  2. Paralysis is shown in uncoordinated movements
  3. Death due to respiratory failure


Tentative diagnosis from the symptoms shown. Isolate suspected foods and carry out tests to identify the toxins and/or the bacteria.


Very difficult to treat. Give the patient antitoxins and treat the symptoms.

Control measure in animals

  • Vaccination protects the animals
  • Avoid feeding the animals on decaying hay/forage.

Control measures in man

Take great care with animal protein foods. Avoid eating cold food preserved from the previous day. Thoroughly heat it up before eating.

3. Clostridium pufringens intoxication

In animals, these bacteria produce toxins type A, B, C, D, and F. it causes what is known as enterotoxaemias.

It usually affects young animals and usually leads to high mortality rates.

Toxin A enterotoxaemia is very rare in animals. In people, they will get it when they eat preserved animal protein without sufficiently heating it first.

Conditions for toxin production

  1. Optimum temperature is usually between 42°C and 47°C.
  2. A pH level of above 6
  3. Salt concentration of about 6 percent.

Large chunks of meat are a perfect harbour for the toxins from C. pufringens. Salting of meat will help in preservation.


Incubation period is shorter; takes an average of 12 hours.

Normal signs of intoxication include:

  • Nausea
  • Abdominal pains
  • Headache
  • Fever
  • Diarrhoea


You can get the toxin from the faeces. Isolate bacteria by culturing.

Control measures in animals

Vaccination is effective

Control measures in man

  1. Be careful when preserving foods with animal protein
  2. Cook food properly, especially animal protein

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Food Scientist | Interested in Data Science for Quality Management | Learning python | Agribusiness consultant with special interest in food processing and quality assurance. | Solve this if you can - if a ship had 26 goats and 10 sheep onboard, how old is the ship's captain?