Food infection occurs when a pathogen enters the gastrointestinal tract and
multiplies. Microorganisms can penetrate into the intestinal mucosa and grow
there, or they can pass through other systemic organs. Infections are
characterized by a delay in the appearance of gastrointestinal disturbance while
the pathogen increases in numbers or affects invaded tissue.
There is also
usually a fever, one of the body’s general responses to an infective organism.
Foodborne infections remain a major public health problem. The Council for
Agricultural Science and Technology estimated in its 1994 report, Foodborne
Pathogens: Risks and Consequences, that as many as 9,000 deaths and 6.5 to
33 million illnesses in the United States each year are food-related.
diseases and infections which are naturally transmitted between vertebrate
animals and man”.
contact with bedding or animals, etc.
reservoir for many diseases common to domestic animals and humans. Persons
working with wildlife should be alert to the potential for disease transmission
zoonotic diseases are so common in nature, so rare in humans, or so mild in
their symptoms, that wild animals pose a minimal health risk to people.
inhalation or contact with infected animal products, soil, water, or other
environmental surfaces which have been contaminated with animal waste
or a dead animal (e.g. salmonellosis, leptospirosis, anthrax). Campylobacter
infection is mainly found in chicken meat. Listeriosis and E.coli
gastroenteritis are two other common infections caused by zoonotic agents.
All these will be discussed one by one.
arthropod to transmit the disease to humans (e.g. St. Louis encephalitis,
Rocky Mountain spotted fever).
Salmonellosis (Salmonella gastroenteritis) results from the ingestion of foods
that contain significant numbers of viable cells of the members of the genus
Salmonella. It is the most frequently occurring food borne infection.
ferment glucose, usually with gas, but usually do not ferment lactose or
sucrose. They are widely distributed in nature, with humans and animals being
their primary reservoir. Generally large number of salmonellae typically 106
bacterium must be ingested to cause illness.
such as birds, reptiles, farm animals, humans and occasionally insects. As
intestinal form, the organisms are excreted in feces from which they maybe
transmitted by insects and other living creatures to a large number of places,
polluted water and contaminated food.
actual infected cases of the disease or from carriers. A carrier is defined as a
person or an animal that repeatedly sheds bacteria, usually through feces,
without showing any signs or symptoms of the disease.
and mice may contaminate unprotected foods with their feces and thus spread
Salmonella bacteria. Flies may play an important role in the spread of
Salmonella, especially from contaminated fecal matter to foods. Humans
acquire the bacteria from contaminated food such as beef products, poultry,
eggs, egg products or water.
the organism and the total number of bacteria ingested. A longer incubation
period usually distinguishes salmonellosis from staphylococcus poisoning:
usually 12-36 hours for the former and about 2-4 hours for the latter.
vomiting, abdominal pain and diarrhoea that usually appear suddenly. This
may be preceded by a headache and chills. Other evidences of the disease are
watery, greenish-fowl-smelling stools, prostration, muscular weakness,
faintness, usually a moderate fever, restlessness, twitching and drowsiness.
mortality is less than 1%. Intesibility may vary from slight discomfort and
diarrhoea to death in 2 to 6 days. About 0.2 to 5.0% of the patients may
become carriers of the Salmonella organism. During the acute phase of the
disease, as many as one billion salmonellae can be found per gram of feces.
shrimp, coconut, sauces and salad dressings, cake mixes, cocoa, peanut butter
Conditions Necessary for Outbreak
These bacteria must be there in considerable numbers i.e., food should be a
good culture media, temperature favourable and enough time allowed for
requires the following:
grossly infected with salmonellae.
that all portions reach 66ºC for 12-15 minutes will assure destruction of
even most resistant Salmonella types.
avoiding prolonged holding of these foods at room temperature.
ENTEROPATHOGENIC ESCHERICHIA COLI
intestinal tract and that of many animals. Serotypes of E. coli which have been
implicated in human diarrhoeal diseases or food poisoning outbreaks and have
been designated enteropathogenic E. coli (EEC).
of temperatures, 20-40ºC with a minimum growth temperature at 10ºC and an
optimum at 37ºC. Heating at 65ºC for 15-20 minutes is lethal. The pH range for
growth is 4.2-8.50, with an optimum in the range of pH 7.2-7.5. E. coli will
grow in the presence of 5.0% salt at 37ºC but 10% is inhibitory.
-1010 viable cells/g that must colonize the small intestine and produce
enterotoxin. The syndrome is characterized primarily by non-bloody, watery
diarrhoea without inflammatory exudates in stools. Incubation time of disease is around 2 days after eating the contaminated food and may last for 8 days.
Common symptoms included are cramps, chills, vomiting, aches and headache.
variety of foods such as cream pie, mashed potatoes, cream puffs and creamed
fish. Other E. coli food poisoning outbreaks have been attributed to the
consumption of milk, cheese, ice cream, meats, fish and macaroni. E. coli is
relatively sensitive to destruction by drying or freezing but some survivors may
exist for extended periods.
gastroenteritis in newborns and in infants up to two years of age.
“Enteroinvasive” strains invade the epithelial cells of large intestine and cause
diarrhoea in older children and adults.
producing) strains produce one or both of two different toxins:a heat stable
toxin (ST) and a heat labile toxin (LT). Both toxins cause diarrhoea in adults
and infants. Enterotoxigenic strains of E. coli are often associated with
Travellers’ diarrhoea, a common disease contracted by tourists when visiting
travel history and symptoms. Laboratory diagnosis is by isolation of the
bacteria from feces. Treatment is with fluid and electrolytes. Other strains of E.
coli which are usually harmless in their normal habitat (the intestine) can cause
disease when they gain access to other sites or tissues. These diseases include
urinary tract infections, septic infections, bacteremia, meningitis, pulmonary
infections, abscesses, skin and wound infections.
have high coliform counts, avoiding unpasteurized juices, washing fresh fruits
and vegetables thoroughly before eating raw, using adequate cooking
procedures for destruction and prompt refrigeration. Most people recover from
E. coli infection within 5-10 days without treatment. Antibiotics and
antidiarrhoeal drugs are usually not helpful.
BACILLUS CEREUS GASTROENTERITIS
aerobic, spore forming rod shaped bacteria normally present in soil, dust and
water. The bacterium has a minimum growth temperature around 4-5ºC, with
maximum around 48-50ºC. Optimum pH range for growth is 4.9 to 9.3.
per gram) of viable cells of
B.cereus must be ingested to develop signs and symptoms of the syndrome.
The bacterial cells produce intoxication characterized by acute abdominal pain,
flatulence and watery diarrhoea.
dehydration and prostration may occur but nausea, vomiting, fever and chills
are rare. The illness appears within 6-15 hours after consumption of food and
the symptoms usually last less than 24 hours.
corn starch, mashed potatoes, vegetables, minced meat, liver sausage, milk,
cooked meat. Food mixtures such as sauces, puddings, soups, pastries and
salads have frequently been incriminated in outbreaks.
ingesting food or water contaminated by fecal material from patients or carriers
(shellfish and plankton may be the natural reservoir).
several hours to three or more days. An infective dose of around one million
organisms should be ingested to cause illness. The bacteria adhere to the small
intestine wall, where they secrete the cholera enterotoxin, choleragen.
result, there is hyper secretion of water and chloride ions, while inhibiting
absorption of sodium ions. The patient experiences an outpouring of fluid and
electrolytes with associated abdominal muscle cramps, vomiting, fever and
liter of fluid during the infection. Death may result from the elevated
concentration of blood proteins, caused by reduced fluid levels, which leads to
circulatory shock and collapse. Onset of the illness is generally sudden, with
incubation periods varying from 6 hours to 5 days.
resulting in contaminated water supplies. Sporadic cases occur when shellfish
harvested from fecally polluted coastal waters are consumed raw.
organism from the diarrheic stools of infected individuals.
Other safe beverages include tea and coffee made with boiled water and
carbonated, bottled beverages with no ice.
fruit that you have peeled yourself.
with NaCl plus sucrose, sodium bicarbonate and potassium chloride to
stimulate water uptake by the intestine. The antibiotics of choice are a
tetracycline or aproflaxin.
proper sanitation, especially of water supplies. The mortality rate without
treatment is often over 50%. Medical treatment to prevent dehydration prevents