12.4.2 Diseases that may be transmitted from milk cows
Bovine tuberculosis (bovine TB) is a very common infection of cattle. It is caused by the bacterium Mycobacterium bovis. Infection may be acquired by drinking raw milk from a cow that has bovine TB. The disease may reach the milk by contamination with faeces or from the coughs of infected cows. Diseased humans can also contaminate the milk during handling. Milk, therefore, should always be pasteurised or sterilised before drinking. Raw milk is the usual cause of the forms of human TB that affect parts of the body other than the lungs.
Brucellosis is an infectious disease characterised by a high fever. It is caused by bacteria belonging to the Brucella genus, mostly Brucella melitensis (a disease of goats) and also Brucella abortus (a disease of cattle) and Brucella suis (a disease of pigs). It occurs mostly as a result of ingestion of contaminated milk and dairy products (such as cheese) from animals infected with Brucella. Brucellosis can also be transmitted by blood, urine or tissues of sick animals, so good hygiene must be maintained at all times around animals.
Q fever is an infection caused by the bacteria Coxiella burnetii (formerly Rickettsia burnetii). Its name derives from the time when the cause of the fever was unknown – the ‘Q’ stands for ‘query’. Only one bacterium is needed to cause the Q fever infection! The disease is transmitted through drinking the raw milk of infected cattle, goat or sheep, and it can also be transmitted in airborne droplets.
As you read earlier, anthrax is usually caused by spores of the bacterium Bacillus anthracis. The spores can remain in soil and dust for a long time and they can infect milk. The spores usually reach the milk via infected blood contaminating the milk, or by dust from the animal’s coat or the environment.