Non Bacterial Microbiological Contamination Of Food

 Microbiological contamination of food may include food borne illness due to
bacteria or non bacterial sources such as mycotoxins, viruses, rickettsias,
parasitic worms or protozoa or from the consumption of food contaminated
with toxic substances. The food borne infections caused by bacteria will be
dealt with in Unit 3 in detail.

Non Bacterial Microbiological Contamination Of Food


Much less is known about the incidence of viruses in foods than about bacteria
and fungi because they do not grow in culture media as do bacteria and fungi,
they do not replicate in foods thus found in low numbers. It is noted that
virtually any food can serve as a vehicle for virus transmission. The most
common food source of gastroenteritis causing virus is shellfish.

Hepatitis A virus

There are more documented outbreaks of hepatitis A traced to foods than any
other viral infection. The virus causes hepatitis (jaundice) and leads to
inflammation of liver. The incubation period for infectious hepatitis ranges
from 15 to 45 days and lifetime immunity usually occurs after an attack. 
fecal-oral route is the mode of transmission, and raw or partially cooked
shellfish from polluted waters is the most common vehicle food. Shellfish are
able to concentrate the numbers of bacteria or viruses during their normal
feeding, which is to filter and remove particles from the water. 
The infectious
hepatitis virus has been shown to be stable during refrigerated storage of
shellfish. In addition to shellfish, raw milk, potato salad, sandwiches and cold
meat cuts are also probable sources of the virus. Symptoms of jaundice include
loss of appetite, yellowing of eyes, nails and skin (due to presence of bile
pigments) and gastrointestinal disorder. Proper cooking, hygiene, sanitation
and personnel cleanliness help to prevent virus attack

Polio Virus

There are a large number of reported food-borne outbreaks of polio in India. It
is most common in children up to 5 years. Milk is the most probable food there
causes spread of polio virus. The virus reproduces in the intestinal tract, from
there it invades the motor cells of the central nervous system. Initial symptoms
are gastrointestinal, headache, muscle pain and paralysis. 
The paralytic
symptoms range from sub clinical to fatal. Preventive measures include
immunization of children, proper processing (pasteurization) of milk, hygienic
conditions and use of potable water.

Norwalk Virus and Norwalk-like Viruses

These viruses, also known as small round structured viruses or caliciviruses,
are an important cause of gastrointestinal illness throughout the United States.
Members of this category of viruses are typically named for the location in
which they were first identified, for example, Hawaii, Snow Mountain,
Montgomery County and Oklahoma. The Norwalk virus is the prototype for
this group of viruses – there are at least 11 other related viruses – hence the
name “Norwalk-like virus.” 
Symptoms: The signs and symptoms of Norwalk-like viruses include nausea,
vomiting, diarrhea, abdominal pain, muscle aches, headache, tiredness and
low-grade fever. Symptoms typically last 24 hours to 48 hours and subside on
their own. There are no known long-term effects after recovery from this
Transmission of viruses: Humans are the only source for these viruses. These
viruses do not multiply outside the human body. The viruses are present in the
feces of infected persons and can be transmitted to others when hands are not
thoroughly washed after having a bowel movement.


Rickettsias maybe considered as degenerative bacteria since they represent a
form of life closely resembling bacteria except that they cannot be cultivated
outside of living cells. Like the viruses they are obligate parasites. Many of the
major human rickettsial diseases are by bites from fleas, lice or ticks. 
Examples of human rickettsial diseases include epidemic typhus, rickettsial pox, Rocky mountain spotted fever and Q fever. Cows infected with rickettsia
of Q fever, Coxiella brunettii excrete contaminated milk which result in human
infections. Hence milk is pasteurized at a minimum temperature of 62.8ºC for
30 minutes to ensure its destruction.

Food Borne Parasites


Trichinella spiralis causes trichinosis, which results from the consumption of
raw or incompletely cooked pork containing the encysted larvae
Symptoms: One or two days after ingestion of heavily encysted meat,
trichinae penetrate the intestinal mucosa, producing nausea, abdominal pain,
diarrhea and sometimes vomiting. The symptoms may persist for several days. 
The larvae then attack the skeletal muscles, muscle pain (paralysis) is the
universal symptom accompanied in difficulty in breathing, chewing and
swallowing. After six months of initial infection, pain, swelling and fever
Prevention and control: Chief method for prevention of trichinosis is the
treatment of pork (or other meat) to ensure the destruction of any trichinae that
maybe present by cooking of pork till at least 58.3ºC, quick freezing or storage
at -15ºC or lower for not less than 20 days, irradiating or processing of sausage
and similar meat products properly by salting, drying, smoking and
Also trichinosis can be controlled by avoiding feeding of infected
meat scraps to swine and by preventing the consumption of infested tissue by
other animals.


Entamoeba histolytica is a single celled parasitic animal – a protozoa, that
infects predominantly humans and other primates and causes amoebiasis.
Diverse mammals such as dogs and cats can become infected but usually do
not shed cysts (the environmental survival form of the organism) with their
feces, thus do not contribute significantly to transmission. 
The active
(trophozoite) stage exists only in the host and in fresh feces; cysts survive
outside the host in water and soil and on foods, especially under moist
conditions on the latter. When swallowed they cause infections by excysting
(to the trophozoite stage) in the digestive tract (amoebiasis).
Symptoms: Infections that sometimes last for years may be accompanied by 1)
no symptoms, 2) vague gastrointestinal distress, 3) dysentery (with blood and
mucus). Most infections occur in the digestive tract but other tissues may be
invaded. Complications include 4) ulcerative and abscess pain and, rarely, 5)
intestinal blockage. Onset time is highly variable. 
It is theorized that the
absence of symptoms or their intensity varies with such factors as 1) strain of
amoeba, 2) immune health of the host, and 3) associated bacteria and, perhaps,
viruses. The amoeba’s enzymes help it to penetrate and digest human tissues; it
secretes toxic substances.
Diagnosis: The ingestion of one viable cyst can cause an infection. Human
cases are diagnosed by finding cysts shed with the stool; various flotation or
sedimentation procedures have been developed to recover the cysts from fecal
matter; stains (including fluorescent antibody) help to visualize the isolated
cysts for microscopic examination. Since cysts are not shed constantly, a minimum of 3 stools should be examined.
In heavy infections, the motile form
(the trophozoite) can be seen in fresh feces. Serological tests exist for longterm infections. It is important to distinguish the E. histolytica cyst from the
cysts of nonpathogenic intestinal protozoa by its appearance.
Transmission: Amebiasis is transmitted by fecal contamination of drinking
water and foods, but also by direct contact with dirty hands or objects as well
as by sexual contact.


Giardia lamblia (intestinalis) is a single celled animal, i.e., a protozoa, that
moves with the aid of five flagella. Organisms that appear identical to those
that cause human illness have been isolated from domestic animals (dogs and
cats) and wild animals (beavers and bears). 
A related but morphologically
distinct organism infects rodents, although rodents may be infected with
human isolates in the laboratory. Human giardiasis may involve diarrhea
within 1 week of ingestion of the cyst, which is the environmental survival
form and infective stage of the organism
Symptoms: Normally illness lasts for 1 to 2 weeks, but there are cases of
chronic infections lasting months to years. Chronic cases, both those with
defined immune deficiencies and those without, are difficult to treat. The
disease mechanism is unknown, with some investigators reporting that the
organism produces a toxin while others are unable to confirm its existence. 
organism has been demonstrated inside host cells in the duodenum, but most
investigators think this is such an infrequent occurrence that it is not
responsible for disease symptoms. Mechanical obstruction of the absorptive
surface of the intestine has been proposed as a possible pathogenic mechanism,
as has a synergistic relationship with some of the intestinal flora.
Diagnosis: Giardia lamblia is frequently diagnosed by visualizing the
organism, either the trophozoite (active reproducing form) or the cyst (the
resting stage that is resistant to adverse environmental conditions) in stained
preparations or unstained wet mounts with the aid of a microscope. 
commercial fluorescent antibody kit is available to stain the organism.
Organisms may be concentrated by sedimentation or flotation; however, these
procedures reduce the number of recognizable organisms in the sample.
Associated foods: Giardiasis is most frequently associated with the
consumption of contaminated water. Outbreaks have been traced to food
contamination by infected or infested food handlers, and the possibility of
infections from contaminated vegetables that are eaten raw cannot be excluded.
Cool moist conditions favor the survival of the organism.
Prevalence: Giardiasis is more prevalent in children than in adults, possibly
because many individuals seem to have a lasting immunity after infection. This
organism is implicated in 25% of the cases of gastrointestinal disease and may
be present asymptomatically. 
This disease afflicts many homosexual men, both
HIV-positive and HIV-negative individuals. This is presumed to be due to
sexual transmission. The disease is also common in child day care centers,
especially those in which diapering is done.


Humans worldwide are infected with Ascaris lumbricoides and Trichuris
trichiura; the eggs of these roundworms (nematode) which are “sticky” and
may be carried to the mouth by hands, other body parts, fomites (inanimate
objects), or foods. 
Ascariasis and trichuriasis are the scientific names of these
infections. Ascariasis is also known commonly as the “large roundworm”
infection and trichuriasis as “whip worm” infection.
Diagnosis: Infection with one or a few Ascaris sp. may be unapparent unless
noticed when passed in the feces, or, on occasion, crawling up into the throat
and trying to exit through the mouth or nose. Infection with numerous worms
may result in a pneumonitis in the lungs, where the larvae break out of the
pulmonary capillaries into the air sacs, ascend into the throat and descend to
the small intestine again where they grow, becoming as large as 31 × 4 cm.
Vague digestive tract discomfort sometimes accompanies the intestinal
infection, but in small children with more than a few worms there may be
intestinal blockage because of the worms’ large size. 
Not all larval or adult
worms stay on the path that is optimal for their development; those that wander
may locate in diverse sites throughout the body and cause complications. Both
infections are diagnosed by finding the typical eggs in the patient’s feces; on
occasion the larval or adult worms are found in the feces or, especially for
Ascaris sp., in the throat, mouth, or nose. 
Associated foods: The eggs of these worms are found in insufficiently treated
sewage-fertilizer and in soils where they embryonate (i.e., larvae develop in
fertilized eggs). The eggs may contaminate crops grown in soil or fertilized
with sewage that has received nonlethal treatment; humans are infected when
such produce is consumed raw. Infected food handlers may contaminate a wide
variety of foods.
Prevention: Both infections may self-cure after the larvae have matured into
adults or may require anthelmintic treatment. In severe cases, surgical removal
may be necessary. Allergic symptoms (especially but not exclusively of the
asthmatic sort) are common in long-lasting infections or upon reinfection in

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