Milk-Borne Infections, Intoxication and toxi-infections:
Despite advances in food processing and preservation, food borne diseases still
constitute a major public health problem. Milk–borne infections and intoxications
share many common features with other food borne diseases but there are
differences which must be considered also. The wide variety of milk products
available to the consumer has added to the potential spread of certain disease
producing agents. The significance of milk in human nutrition is now well
established as it is considered as the best, ideal and complete food for all age
groups. However, inspite of being so, milk can also serve as a potential vehicle for
transmission of some diseases under certain circumstances. Moreover, by virtue of
processing almost all the essential nutritional factors ,milk can also serve as an
excellent culture and protective medium for certain microorganisms which may
include potential pathogens capable of causing serious health problem to the
consumers. Milk serves as an excellent culture medium for many microorganisms,
particularly bacteria, whose multiplication is mainly dependent on temperature and
competing microorganisms. Milk also serves as a ready and efficient vehicle for a
great variety of infectious and non- infectious agents. With the advent of mass
collection and distribution, this potential for disease transmission has become a
significant community problem. In this way, milk may serve not only as a vehicle
of transmission of disease causing organisms, but it can also allow these pathogens
to grow, multiply and produce certain toxic metabolites, thereby, milking itself an
extremely vulnerable commodity from public health point of view. A variety of
pathogenic organisms may gain access into milk and milk products from different
sources and cause different types of food-borne illness. Milk and milk products
may carry organisms as such or their toxic metabolites (poisoning), called ″toxins″
to the sensitive consumers. Ingestion of toxins already synthesized in the food (i.e.
pre-formed) brings about poisoning syndromes in the consumers. This is called
″Food intoxication″ and the toxins affecting the gastro-intestinal tract are called
enterotoxins. On the other hand, the ingestion of viable pathogenic bacteria along
with the food leads to their lodgement and establishment in consumer’s organs.
This is termed as ″Food infection″. There are yet other types of organisms which
can infect the intestine when ingested along with the food and produce toxins in
situs to bring about symptoms of
poisoning. The situation is called ″toxi-
infection″. These three categories are better covered by the term ″Food-borne
infections and intoxications″. Apart from these food-borne illnesses chiefly
bacterial types, a number of other types of diseases whose aetiological agents of
disease may be bacteria, fungi, recketsiae, and viruses can also spread through milk
and milk products. The microbiological health hazards arising from the
consumption of contaminated high risk foods like milk has grown in recent years
and has resulted in national and international intensification of food hygiene
programmes. Although the occurrence of incidences of food-borne illness has been
considerably reduced in most of the developed countries chiefly due to adoption of
strict microbiological quality control / and sanitary practices during the production,
processing and distribution of milk and milk products, the situation continues to be
grim in developing countries like Iraq where such practices are impractical. This
coupled with heavy expansion of dairy industry in the third world countries, has
actually increased such risk of milk-borne intoxications and other illness. Such
food- borne illnesses and diseases and their respective causative agents have been
listed in the following table 12.
Table 12: Common milk-borne infections, intoxications and
infections
toxi –
Type
of
milk-borne Causative agent
isease /disorder
disease
A-Food infection
Salmonella typhi & related Typhoid,
Salmonellosis
species
(Food poisoning ).
Shigella dysenteriae
Shigellosis (dysentery)
Streptococcus
Septic sore throat scarlet
fever food poisoning.
species(enterococci)
B-Food Intoxication:
1- Bacterial type
2-Fungal type
Staph. aureus
Food poisoning
Cl. botulinum
Botulism (food poisoning).
E. coli
Summer diarrhea
Vibrio Cholera
Cholera.
Aspergillus flavus
A flatoxicosis.
Other toxigenic
Mycotoxicosis.
Mold species
C-Toxi-infection
Type
disease
of
Bacillus cereus
Food poisoning
Cl. perfringens
Gas gangrene
milk-borne Causative agent
Disease /disorder
D- Other milk –borne Aeromonas species.
Food poisoning.
disorders.
Proteus species.
Food poisoning.
(Uncertain pathogensis)
Kelebsiella species
Food poisoning.
Pseudomonas species.
Food poisoning.
Citrobacter species.
Food poisoning.
E- New emerging
Listeria monocytogenes
Listeriosis.
pathogens
Yersinia enterocolitica
Diarrheal diseases
Campylobacter jejuni
Diarrheal diseases
Vibrio parahaemolyticus
Diarrheal diseases
F-
Other
disease:
1-Bacterial
milk-borne Mycobacterium
tuberculosis
Tuberculosis.
Brucellosis
Brucella abourtus
Brucellosis
Brucella melitensis
Corynebacterium
diphtheriae
Diphtheria
Anthrax.
Bacillus antharacis
2- Rickettsial
Coxiella burnetii
Q –fever.
3- Viral
Entro viruses
Enteric fever.
Infectious hepatitis virus
Infectious hepatitis
Tick-borne encephalitis virus
Tick- borne encephalitis
Foot and mouth disease
Virus (FMD virus)
Foot and mouth disease
(FMD).
The pathogenic organism may be introduced into milk from the following:
I- Dairy animals (Cows).
II- Milk handlers.
III- Environment.
I-Dairy animals (Cows):
Infectious agent may be present in milk as a result of infections in cows. The
organisms may be transmitted to milk either directly from the udder or indirectly
through the infected body discharnges which may drop, splash or be blown into
milk. These organisms can be excreted through the mammary gland directly into
the milk or they may originate from the skin, the mucous membranes or the
intestinal tract of the Cow.
Major diseases of animal origin:
1- Brucellosis.
2-Bovine tuberculosis.
3- Salmonellosis.
4- Q- Fever.
5-Campylobacter enteritis.
Occasional diseases of animal origin:
1-Leptospirosis.
2-Listeriosis.
3-Yersiniosis.
4-Streptococcus agalactiae infection.
5- Foot and mouth disease (FMd).
6- Anthrax.
7-Cow pox.
II- Human handlers or milk handlers:
The diseased persons may transmit diseases by contaminated hands or by
coughing, sneezing and talking. Milk handlers may introduce pathogenic
organisms into milk at many different points between production and packaging.
Recontamination of milk after pasteurization or sterilization is of particular
importance. Many enteropathogenic organisms are shed intermittently by the
carriers.
Milk –borne disease of human origin:
A number of major diseases of human origin may be transmitted through milk and
typhoid is in this category.
A-Bacterial diseases of human origin:
1- Typhoid.
2- Paratyphoid.
3- Cholera.
4- Diphtheria.
5- Shigellosis (Dysentery).
6-Streptococcus pygenes infection:
-Scarlet fever.
- Septic Sore Throat.
7- Staphylococcal enterotoxaemia.
8- Human tuberculosis (TB).
B-Viral disease of human origin:
1 -Poliomyelitis.
2 –Hepatitis A.
III-Environment:
Dairy and farm environment may also introduce a variety of pathogens into milk
and milk products at different stages of production and processing. Some of the
common air-borne pathogens include Group A streptococci, Corynebacterium
diphtheria, Mycobacterium tuberculosis, Coxiella burnetti and some viruses of
respiratory origin. Water, Fooder and un hygienic conditions at farm and plant
level may also contribute pathogens in milk.
Water used for
↓
↓
Cows (washing udder)
↓
Equipment &
utensils
Milk handlers
Environment
↓
↓
Dust
Air
↓
Insects
↓
Rodents
↓
↓
Manure
urine
Preventation and control of milk–borne diseases is one of the most important
problems of public health. Success in controlling a disease can be maintained only
by the constant vigilance over the health of dairy animals and by the adequate
controls at all points from the time milk leaves the cow udder until it reaches the
mouth of the consumers. Before understanding the details of a food-borne illness,
one must be fully acquainted with the following terms used quite frequently during
the description of such disease.
Outbreak: In food –borne disease is defined as an incident in which two or more
persons experience a similar illness usually gastro-intestinal after ingestion of a
common food. In case of Botulism; involvement of even one person constitutes an
outbreak.
Epidemiology: A systemic approach to locate the cause and mode of transmission
of the disease so that the corrective measures can be applied.
Aetiology: Identification of the causative agent of the disease through laboratory
diagnosis.
a- Investigation of outbreaks:
For investigation of an outbreak the following steps are to be followed:
1-A detailed description of gastro-intestinal cases should be made.
2-A record should be made of food eaten and a common source of
should be identified if several or large number of individuals is involved.
infection
3-History of the previous illness of the personnel handling milk and milk
products should be found out.
4-Evidence of enteric disorders, Scratches, wounds, sores, pyogenic
other evidence of sepsis should be looked for and where
infections or
indicated swabs should
be taken.
5-Sanitary facilities and practices used in the plant or shops should be recorded.
6-If a particular farm is suspected, a detailed Veterinary record of animals Should
be obtained with particular attention to recent cases of mastitis.
7- Pooled milk samples from one or several animals should be taken
immediately cooled and held cool until delivered to the
aseptically,
laboratory for
examination.
8- After identification of the suspected animals carrying the causative
the individual samples should be obtained.
organisms,
9-All suspected specimens of milk or milk products should be collected
examination.
for
b- Reporting of milk –borne infections:
Milk–borne infections and intoxications should be made notifiable and reported by
National Authorities according to the standard classification commonly followed.
A-Milk –borne infections:
A great variety of bacteria can produce specific types of milk –
and may subsequently lead to food–poisoning outbreaks
pathogens, which can cause a variety of food
milk and milk products, the
1- Salmonellosis:
borne illness
among the bacterial
infections through the ingestion of
following types are more prevalent:
It is a disease resulting from the ingestion of Salmonella along with the
contaminated food.This is mainly a food–borne illness and milk and milk products
appear to be commonly implicated. It is during the mishandling of the milk and
milk products that the causative organisms of the disease may enter these products.
While milk and milk products can allow salmonella to grow but proper care in the
production, processing, preparation, handling and storage of these foods will
reduce the chances of Salmonella outbreaks. Salmonellosis is considered an
infection since large number of Salmonellae are needed to cause the human illness
and no toxic product is involved and such number are only reached when the
organism multiply in food (105 - 107 organism / ml are required to cause an
infection).
Causative organisms: Although there are a number of different types of
salmonella which can cause salmonellosis, the involvement of the following is
more common (Table 13).
Table 13: Types of Salmonella which can cause Salmonellosis
Organism
Disease/disorder
Salmonella typhi
Typhoid fever
Salmonella paratyphi A
Paratyphoid fever
Salmonella paratyphi B
Paratyphoid fever
Salmonella schtmuelleri
Paratyphoid fever
Salmonella entertiidis
Food poisoning
Salmonella weltiverdin
Food poisoning
Salmonella typhimurium
Food poisoning
The majority of the cases of milk-borne salmonellosis usually derive from cows.
However, typhoid is restricted to man (not pathogenic to animals) and therefore
only spread directly or indirectly by contamination of milk by human carriers.
Sources of causative organisms:
The following sources may introduce salmonella in milk and milk products.
1-water: it is the most important source of Salmonella as it frequently
contaminated through fecal matter. If polluted water with fecal
for washing of utensils and equipment; it can lead to
and milk product. Soilage of cows in polluted
gets
matter is used
contamination of milk
water is another source.
2-Handlers: The next important source is the handlers (farm, distributing
etc.) who are symptomless carriers or active cases.
plant
3-Intermediate persons: can also sometimes be responsible.
4-Flies: whose bodies have become contaminated with human excreta also act as
a source of contamination.
5-Animals: Animals suffering from Salmonellosis can under certain conditions
excrete viable organisms in their milk.
6- Dust.
7- Concentrates.
8- Rodents.
Although clinical salmonellosis in animals may be characterized by septicaemia,
gastroenteritis and abortion, the majority of animals that are infected with
Salmonella are symptomless carriers. Occasionally cows suffering from clinical
Salmonellosis may excrete Salmonella in the milk, but in most cases infection
derives from faeces of carrier or sick animals.
Table 14: Incidence of Salmonella in dairy products and market sweet samples
Milk
product
NO. of samples
Salmonella serotypes
Tested
Positive
NO.
species
Raw cream
37
5
3
2
Salmonella enteritidis
Salmonella dublin
Salted
Butter
Cheese
12
-
-
-
15
2
1
1
Salmonella enteritidis
Salmonella dublin
Dalhi
In India
22
3
3
Salmonella enteritidis
Disease in relation to human beings:
Salmonella can produce three types of milk –borne diseases, namely:
a-Typhoid.
b-Paratyphoid.
c-Food poisoning.
Typhoid and paratyphoid are caused in man by Salmonellia typhi and Salmonella
paratyphi. Almost all species of salmonella are pathogenic to human. However,
organisms of typhoid and para typoid are not pathogenic to animals.
Symptoms:
a- Typhoid fever:
It is characterized by continued fever, inflammation of the intestine, formation of
intestinal ulcers, enlargement of spleen ,characteristic rose spot eruption on the
abdomen and toxaemia.
b- Paratyphoid fever:
In general, it resembles typhoid fever but it is mildler than typhoid fever.
Approximately 105-107 organisms / ml are required to cause infection.
C-Salmonella-food poisoning:
Symptoms are nausea, vomiting, abdominal pain, diarrhea, chills, headach,
prostration, muscular weakness, drowzines, moderate fever, restlessness etc. The
species involved are:
-Salmonella enteritidis.
- Salmonella typhimurium and
- Salmonella weltiverdin .
Incubation period: It various from 7-14 days for typhoid fever and 1-7 days for
paratyphoid fever.
Diagnosis: Organisms may be present in faeces, urine and blood and are
identified by microscopic, cultural, fermentative and serological tests. Diagnosis of
the disease can also be made by the observation of typical symptoms.
Susceptibility and Immunity: Some people are naturally immune whereas a few
become immune after the recovery from disease (Acquired immunity). Active
artificial immunity of about 2 years is developed as a result of typhoid.
Preventation and control: Some of the common preventive and control measures
used for eradication of this disease are:
1- Adequate treatment of water supply.
2-Infected individuals who had infection should not be allowed to handle
milk
and milk products.
3-Following the hygienic conditions during production, processing and storage of
milk and milk products.
4- Educating people about food and personnel hygiene.
5- Following rigid sanitary practices in dairy and retail shops.
6-Periodic examination of individuals who handle foods for public consumption
and elimination of carriers.
7-Pasteurization of milk and milk products and other adequate heat
treatment
with proper storage temperature at retail outlets.
8-Control of flies.
9- Immunization of population by use of vaccine.
10- Vaccination of susceptible members in the family of a patient.
11- Infected individuals should be isolated. All bowel and urinary
discharges
should be disinfected.
12-Treatment of infected individuals with chloramphenicol
administration.
13- Prevent recontamination of milk by Salmonella after processing.
14-Detection and elimination of carrier animals.
2-Bacillary dysentery (Shigellosis):
Shigellosis is one of the common food-borne infections caused by Shigella. Milk
has been invariably found to be responsible for the transmission of this disease.
Milk –borne outbreaks have been frequently recorded and unpasteurized milk
appears to be commonly implicated in such outbreaks. Shigella dysenteriae and
Shigella sonni, the two common types of Shigella, multiply readily in milk at
temperature of 15°C or above. This multiplication is much more pronounced and
the organisms remain viable for a long period in pasteurized than in raw milk.
Causative organisms: The following three species of Shigella are more commonly
involved in shigellosis and cause enterocolitis:
- Shigella dysenteriae
-Shigella sonni
-Shigella flexneri
Sources of the causative organisms:
a- Milk may become infected by contamination with infected materials like
utensils, water, flies.*etc.
b- Milk handlers (carriers) may also cause contamination.
*Note:
Flies that have had contact with infective human excreta.
Disease in relation to human beings:
Out of the three species Shigella dysenteriae causes the most severe disease as it
produces a possible endotoxin.
Symptoms: Shigellosis is an acute intestinal disease characterized by diarrhea with
blood, pus or mucus, fever, vomiting, abdominal cramps and tenesmus.
Diagnosis: Diagnosis is made by the isolation of the organism (by taking rectal
swabs and plating on desoxycholate citrate agar) and conducting certain
biochemical tests.
Susceptibility and Immunity:
Immunity following the disease is slight and of
short duration. There are no means of establishing artificial active immunity.
Incubation period: It is usually for 4 days (1-7days).
Preventation and control: The following control measures should be adopted for
minimizing the incidences of milk-borne Shigellosis:
a-
Rigid
sanitary
discipline
should
be
enforced
in
dairy
workers
particularly in pasteurization plants and retail shops dispensing milk in bulk.
c-
All the attendants looking after the patients should be prohibited from
contact with milk or utensils.
d- Take precautions to exclude flies (control of flies).
e- Pasteurization of milk and milk products
f- Infected individuals should not be allowed to handle milk and milk
products.
3-Streptococcal infections:
Streptococcal infections like septic sore throat, scarlet fever and food poisoning
have been traced to the consumption of milk and milk products. Human beings and
animals both are responsible for the contamination of milk with streptococci.
Although there has been lot of debate regarding streptococcal food poisoning
through milk and milk products, a few strains of group D streptococci or
enterococci have been found to produce toxic metabolites in milk and their
toxigenic potentials have been ascertained in laboratory animal models.
Causative agents:
a-Streptococcus pyogenes (Haemolytic streptococci of human origin)
causes the 1 - scarlet fever
2 - septic sore throat
3- Tonsillitis.
4- septicaemia.
b-Streptococcus agalactiae :
Causes mastitis in animals.
c- Group D streptococci:
(Enterococci = Streptoccus faecalis)
Causes food poisoning.
Note: Streptoccus pyogenes which are of human origin organisms introduced
through the lumens of the teats from the hands of infected milkers may reproduce
in udders.
Sources of the causative organisms:
a- Animals infected with Strept. agalactiae may harbour the organisms in
udders (mastitis) and act as a source of pathogen.
b- The personnal directly connected with the care and milking of animal in a
dairy herd may act as vectors of mastitis and cause mastitis in other
animals as they carry the pathogens on skin of hands.e.tc.
c- Entercocci are chiefly of fecal origin and fecal contamination of milk and
milk products may introduce lot of enterococci in these products.
a- Milking machines may help in the transfer of pathogens (Strept.
agalactiae) to milk and also to another animals with the help of infected
teat cups.
b- Human carriers of Streptococcus pyogenes (which is pathogenic to man)
contaminate milk and milk products during handling and
processing.
c- Human carriers disseminating the pathogenic Strept .pyogenes may also
infect animals which develop clinical or subclinical udder infections and in
turn, pass streptococci to milk, out of these streptococci in milk, such milk,
if consumed raw or insufficiently heat treated, can act as a source of
sporadic or epidemic cases. So scarlet fever and tonsillitis from
Streptococci passing into milk from infected lesions on the udder and on
teats of cows.
d- Milk products may get contaminated from raw milk infected with
Streptococci. Butter has been found to contain viable organisms even after
six months and cheese after 18 weeks of refrigerated storage.
Disease in relation to human beings:
Streptococcus pyogenes has been known to be pathogenic to human being whereas
Strept. Agalactiae is not. Streptococcus pyogenes causes septic sore throat, scarlet
fever etc. Enterococci (Strept .faecalis var faecalis)
liquefaciens, Strept. faecalis var
Strep. faecalis var
zymogenes. and Streptococcus faecalis may
cause food poisoning in human beings.
Symptoms:
I-Septic sore throat: It is characterized by high and irregular fever, sudden onset
of fever, inflammation and swelling of lymph glands of throat and sometimes
involving the formation of Abscesses around the tonsils and in the cervical lymph
glands.
II-Scarlet fever:
It is an acute febrile disease of throat accompanied by a scarlet rash. Invasion of
other parts of body may occur by the organism resulting in infections of middle
ear, kidneys, etc. scarlet rash is due to elaboration of a toxin.
III-Food poisoning:
The symptoms resemble Staphylococcal food poisoning syndromes.
However, these are of mild type.
Diagnosis:
I-Septic Sore throat:
Throat swabs should be taken from patients and observed for the
presence of
haemolytic Streptococci of Lancefield group A (Stret. Pyogenes).
II-Scarlet fever: The disease can be diagnosed by clinical symptoms as
well as
by isolation of the organism.
III-Food poisoning: The Streptococcal food poisoning can be diagnosed
isolation of the causative organisms and by their enterotoxin
toxigencity.
by the
typing and their
Susceptibility and immunity:
Immunity against types of one group does not protect against infection by types of
other groups. Bacterial immunity is of temporary duration. Immunity against
scarlet fever is permanent if antitoxin is injected.
Incubation period: 1-3 days
Prevention and control:
1- Adequate heat treatment of milk and milk products.
2-Holding milk at low temperature (7°C).
3-Rejection of milk from suspected milk quarters.
4-Milk showing abnormal changes should not be pooled.
5-Regular check on health of dairy workers.
6-Faecal contamination of milk and milk products should be avoided.