HUMAN DISEASES TRANSMITTED THROUGH MILK

1. Cholera (Vibrio cholerae)

Outbreaks of this disease due to infected milk have been reported in various parts of the world. The infection of milk may be through carriers or through infected water used for adulteration. Human carriers have been proved to be very potent source of infection of the milk. The causative microorganism Vibrio cholerae apparently is easily destroyed by acid development in milk and cream. Prevention consists of periodic medical inspection of all persons connected with farm operations and pasteurization of milk, as the organism is destroyed at 55ºC.

2. Typhoid or Enteric Fever

It is caused by Salmonella typhi. Milk forms the chief source of infection, which occurs through infected persons (active cases) and carriers are potent sources. Use of contaminated water for washing the utensils is another source. Infection through flies is possible. Water obtained from trusted sources largely eliminates the chances of typhoid organisms entering into milk through water. Elimination of human carriers is very important. Pasteurization of milk invariably kills the bacteria.

3. Paratyphoid

The etiological agent is Salmonella paratyphi and spread of this disease through milk and dairy products show similar features as typhoid and the sources of infection are the same as in typhoid. The paratyphoid bacilli are destroyed when the milk is heated to a temperature of 59ºC for 10 minutes.

4. Diphtheria (Causative agent : Corynebacterium diphtheriae)

Milk borne epidemics have been reported from lesions on the teats from which the organisms were isolated. However, the primary sources of the organism have been traced to either the milk man or some farm worker. The organism produces an extra cellular toxin in the respiratory tract of man, which sometimes causes death. The animals got infected secondarily, and the human carrier is an important factor. Prevention consists of rigid medical inspection of all dairy workers and pasteurization of milk makes it safer for human consumption.

5. Streptococcal infections

Streptococcal infections like septic sore throat, scarlet fever and food poisoning have been traced to the consumption of contaminated milk and dairy products. Few strains of group D streptococci and enterococci have been found to produce toxic metabolites in milk.

A. Streptococcus pyogenes

This bacterium causes scarlet fever, septic sore throat, tonsillitis and septicemia in humans.

B. Streptococcus agalactiae

It is the causative agent for mastitis in animals.

C. Group D streptococci

It is one of the pathogen behind incidence of food poisoning in the human beings.

Scarlet fever is primarily a disease of man, but cows may be secondarily infected from human sources and pass on the disease through milk to man. Large number of streptococci shed from udder of single cow infected with this organism may contaminate a large bulk of milk. Pasteurization of milk is the only safeguard against these bacteria.

Control

1. Adequate heat treatment of milk and its products.

2. Holding of milk at low temperature during storage.

3. Rejection of milk from animals suffering from mastitis.

4. Regular check on the health of the dairy workers.

5. Fecal contamination of milk and its products should be avoided.

6. Shigellosis

Shigellosis is one of the common food borne infections caused by Shigella dysenteriae. Milk borne outbreaks have been frequently recorded and unpasteurized milk appears to be commonly implicated in such outbreaks. Shigella multiplies readily in milk at a temperature of 15°C or above.

Milk may become infected by contamination with infected materials like utensils, water, flies, etc. Milk handlers may be carriers of infectious agents and also cause contamination.

Control

Rigid sanitary discipline should be enforced among dairy workers particularly in pasteurization plants and retail shops dispensing milk in bulk. All the sanitary attendants looking after patients should be prohibited from contact with milk or utensils. Fly population should be controlled adequately during milk production and distribution.

7. Listeriosis

Listeriosis is a food-borne illness caused by Listeria monocytogenes, is capable of growing over a wide range of temperatures from 1 to 45°C. The pathogenicity is due to the production of extracellular haemolysin (alpha, beta) by this organism. Infected animals are the main sources of these organisms. Handlers carrying the disease, unhygienic practices during production and processing, faecal contamination of milk and water, contaminated refrigerators, dish and clothes may also introduce the organisms into milk.

This organism appears to survive heat treatments like pasteurization. The possible reason for the survival of this organism is the ingestion of these organisms by leukocytes in milk, which may give some protection against heat treatment. Ingestion of L. monocytogenes through milk and milk products can cause listeriosis in man leading to the death of the consumer. The symptoms of listeriosis are acute meningitis with or without septicemia.

Control

i) Strict hygienic practices should be followed during production and processing.

ii) Prevention of source of infection.

iii) Proper heat treatment of milk.

8. Bacillus cereus poisoning

Bacillus cereus is one of the causative organisms for mastitis. The herd raw milk sometimes gets B. cereus from mastitic animals. The raw milk also gets spores from animal’s teats and skin, milking machine and other source such as cans. Soil may introduce B. cereus directly or indirectly into milk and milk products.

Three types of toxins are elaborated by toxigenic strains of B.cereus in milk and milk products.

1. Haemolysin 2. Lecithinase 3. Enterotoxin.

Enterotoxin is responsible for food poisoning outbreaks, while lecithinase and haemolysin play important role in the pathogenesis of the organism.

Control

Prompt cooling of milk/ product during storage.
General hygienic conditions should be maintained during production of milk and marketing of dairy products.

9. Aflatoxicosis

Aflatoxicosis is common type of fungal intoxication caused by the common moulds Aspergillus flavus and A. parasiticus by virtue of their ability to produce aflatoxin. A. flavus can produce aflatoxin B1, B2 and G1, G2 types in milk and milk products. Upon ingestion, the Aspergillus toxins are metabolized by the milch animals and are secreted into the milk in the form of M1 and M2, which are also toxic to the milk human beings who consume the contaminated milk. These toxins are extremely heat stable, potent and exhibit very strong toxicity apart from being highly carcinogenic.

Aerial contamination is one of the most important sources of mould spores. Soil and contaminated food may also introduce spores in milk and milk products. Poor storage conditions, especially damp weather favour toxin production.