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 toxi –infections
isease /disorder / Causative agent / Type of milk-borne diseaseTyphoid, Salmonellosis (Food poisoning ). / Salmonella typhi& related species / A-Food infection
Shigellosis (dysentery) / Shigella dysenteriae
Septic sore throat scarlet fever food poisoning. / Streptococcus
species(enterococci)
Food poisoning / Staph. aureus / B-Food Intoxication:
1- Bacterial type
Botulism (food poisoning). / Cl. botulinum
Summer diarrhea / E. coli
Cholera. / Vibrio Cholera
A flatoxicosis.
Mycotoxicosis. / Aspergillusflavus
Other toxigenic
Mold species / 2-Fungal type
Food poisoning
Gas gangrene / Bacillus cereus
Cl. perfringens / C-Toxi-infection
Disease /disorder / Causative agent / Type of milk-borne disease
Food poisoning.
Food poisoning.
Food poisoning.
Food poisoning.
Food poisoning. / Aeromonas species.
Proteus species.
Kelebsiella species
Pseudomonas species.
Citrobacter species. / D- Other milk –borne disorders.
(Uncertain pathogensis)
Listeriosis.
Diarrheal diseases
Diarrheal diseases
Diarrheal diseases / Listeria monocytogenes
Yersinia enterocolitica
Campylobacter jejuni
Vibrio parahaemolyticus / E- New emerging
pathogens
Tuberculosis.
Brucellosis
Brucellosis
Diphtheria
Anthrax. / Mycobacterium tuberculosis
Brucella abourtus
Brucella melitensis
Corynebacterium diphtheriae
Bacillus antharacis / F- Other milk-borne disease:
1-Bacterial
Q –fever. / Coxiellaburnetii / 2- Rickettsial
Enteric fever.
Infectious hepatitis
Tick- borne encephalitis
Foot and mouth disease (FMD). / Entro viruses
Infectious hepatitis virus
Tick-borne encephalitis virus
Foot and mouth disease
Virus (FMD virus) / 3- Viral
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, Coxiellaburnettiand 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 & Milk handlers
utensils
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 infection should be identified if several or large number of individuals is involved.
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 infections or other evidence of sepsis should be looked for and where 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 aseptically, immediately cooled and held cool until delivered to the laboratory for examination.
8- After identification of the suspected animals carrying the causative organisms, the individual samples should be obtained.
9-All suspected specimens of milk or milk products should be collected for examination.
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 – borne illness and may subsequently lead to food–poisoning outbreaks among the bacterial pathogens, which can cause a variety of food infections through the ingestion of milk and milk products, the following types are more prevalent:
1- Salmonellosis:
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
Disease/disorder / OrganismTyphoid fever / Salmonella typhi
Paratyphoid fever / Salmonella paratyphi A
Paratyphoid fever / Salmonella paratyphi B
Paratyphoid fever / Salmonella schtmuelleri
Food poisoning / Salmonella entertiidis
Food poisoning / Salmonella weltiverdin
Food poisoning / Salmonella typhimurium
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 gets contaminated through fecal matter. If polluted water with fecal matter is used for washing of utensils and equipment; it can lead to contamination of milk and milk product. Soilage of cows in polluted water is another source.
2-Handlers: The next important source is the handlers (farm, distributing plant etc.) who are symptomless carriers or active cases.
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
Salmonella serotypes / NO. of samples / Milk productspecies / NO. / Positive / Tested
Salmonella enteritidis
Salmonella dublin / 3
2 / 5 / 37 / Raw cream
- / - / - / 12 / Salted Butter
Salmonella enteritidis
Salmonella dublin / 1
1 / 2 / 15 / Cheese
Salmonella enteritidis / 3 / 3 / 22 / Dalhi
In India
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 Salmonelliatyphi and Salmonella paratyphi. Almost all species of salmonella are pathogenic to human. However, organisms of typhoid and paratypoid 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. Shigelladysenteriaeand Shigellasonni, 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 -Shigellasonni -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 Shigelladysenteriae 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.