Sunday, June 8, 2008

Tuberculosis and Mexican cheese

Quite by chance, on the day I was writing my last blog article on raw milk, the Orange County Register published an article by Doug Irving on an outbreak of tuberculosis in San Diego. See

Mycobacterium bovis is relatively rare in humans, but can be serious and difficult to treat. It is thought that the disease jumped from cattle to humans somewhere between 8000 and 4000BC, when cattle were domesticated. There is archaeological evidence that humans suffered the disease, pulmonary tuberculosis, which may have been contracted through consumption of raw milk. The human specialized form M. tuberculosis was probably spread by migrating Indo-Europeans and by 1000BC it had spread to the whole of the known world.

It appears that in the San Diego area, the disease is spreading primarily through the Latino population and scientists there believe that it may be being brought into the country from Mexico in queso fresco, a popular soft crumbly cheese that may be produced as a cottage industry.

The article in the OC Register contains some inaccuracies. Not all milk sold in the USA must be pasteurized; it depends on the particular State legislation. In addition, the article implies that the outbreak has suddenly flared. However, the actual study by UCSD Medical Center and county health officials, showed that between 1994 and 2005, there were 3,291 cases of active infection reported by the county's Tuberculosis Control Program and of those, about 8 percent were ill with M. bovis. Roughly the same pattern was observed in 2007.

The sale of raw milk cheeses in New Zealand is currently limited and subject to strict controls. See

Extra hard Italian Parmesan-style raw milk cheeses like Grana Padano, Pamigiano Reggiano, Romano, Asiago and Montasio have a low water activity of about 0.693, which prevents the growth of bacterial pathogens.

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