There are many species of streptococcal organisms that might be involved with
streptococcal infections, such as strep throat and scarlet fever. The infectious agent of
Q fever is the rickettsial organism Coxiella burnetii.
c. Diseases from Handling and Exposure. Transmission of disease from
other than the cow is usually a result of milk contaminated due to handling procedures
under conditions of uncleanliness of personnel and equipment, and from exposure of
milk to dust or droplets bearing pathogenic microbes. Diseases most commonly
transmitted by contamination of milk from this source are: diptheria, typhoid fever,
salmonellosis (a common source of blood poisoning), shigellosis (bacillary dysentery),
and, again streptococcal infections. (A description of these diseases can be found in
any standard medical reference.) The infectious agents of the above diseases are
respectively: Corynebacterium diphtheriae, Salmonella typhi, other Salmonella species,
Shigella species and Streptococcus species.
CONTROL OF MILK-BORNE DISEASES
a. Techniques. Four techniques are employed for the specific control of milk-
borne diseases. These are:
The inspection of cattle and elimination of infected animals.
Routine medical examination of all milk handlers and dairy personnel.
The killing of disease agents by the process of pasteurization.
(4) Proper temperature control of milk during storage. This technique
serves as a method of lengthening the lag phase of the growth curve of
b. Pasteurization. Pasteurization is the process of heating milk to destroy
pathogenic microbes. This is followed by rapid cooling. Today, most of us invariably
associate pasteurization with milk. However, the process was first devised by Louis
Pasteur not for milk, but to destroy the organisms, which could spoil wine. Now, it is
important primarily as a means of ensuring safe milk since it destroys all pathogens
likely to be present. One of the most difficult disease agents to destroy in milk is the
rickettsial agent, Coxiella burnetii, and the cause of Q fever. A drop of even 4F (2.2C)
in the pasteurization temperature will allow some of these organisms to survive. In
addition to destroying the pathogens in milk, pasteurization causes a marked decrease
in the numbers of nonpathogens, such as Streptococcus lactis and various
Lactobacillus species. This enhances the keeping quality of the milk since it is the lactic
acid formed by the nonpathogens that is responsible for the souring of milk. Therefore,
with fewer organisms, less lactic acid is produced, and the time required for the milk to
sour is increased.