Raw milk: playing with fire

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U.S. citizens enjoy one of the most abundant and safe food supplies in the world. Along with that abundance and affordability comes a lot of choices, and though it’s still a small subset of the population, an increasing number of people are jumping on the raw-milk bandwagon. Proponents advocate that raw milk has more healthy proteins than pasteurized milk, tastes better, is fresher and does not to contribute to a host of diseases (from diarrhea to autism) that they claim pasteurized milk does.

The scientific community, however, including the Centers for Disease Control and Prevention, the American Veterinary Medical Association, the American Medical Association and the Food and Drug Administration (FDA) believe that raw milk consumption is an unsafe practice.

2006 testimony before the House Agriculture Committee of the State of Ohio House of Representatives from John F. Sheehan, Center for Food Safety and Applied Nutrition of the FDA, said:“Raw milk is inherently dangerous and may contain a whole host of pathogens including enterotoxigenic Staphylococcus aureus, Campylobacter jejuni, Salmonella species, Escherichia coli species, Listeria monocytogenes, Mycobacterium tuberculosis, Mycobacterium bovis, Brucella species, Coxiella burnetii and Yersinia enterocolitica, to name a few.” Sheehan noted that though most consumers will not realize it, prior to pasteurization, Mycobacterium bovis was reported to cause between 6%–30% of all tuberculosis cases in the United States.

Recent work published in the January 2009 Clinical Infectious Diseases by Jeffrey T. LeJeune, DVM, PhD, Dipl. ACVM, Ohio Agricultural Research and Development Center and Päivi J. Rajala-Schultz, DVM, PhD, Dipl. ACVPM, The Ohio State University, says that the consumption of milk that is not pasteurized increases the risk of contracting disease from a foodstuff that is otherwise very nutritious and healthy, and that despite concerns to the contrary, pasteurization does not change the nutritional value of milk.

LeJeune and Rajala-Schultz’s paper explains that pasteurization has become the cornerstone of milk safety. Pasteurization is the process of heating milk for a predetermined time at a predetermined temperature to destroy pathogens. The current guidelines for temperature and time combinations for pasteurization are based on the ability of the process to destroy C. burnetii. The thermal destruction process is logarithmic, and bacteria are killed at a rate that is proportional to the number of bacteria present. Pasteurization improves the safety and lengthens the shelf life of a product by destroying pathogenic and spoilage organisms.

Raw-milk advocates claim that pasteurization fundamentally changes the structure of milk components, rendering it less healthful. However, “the claims of raw-milk advocates are mostly anecdotal and are not supported by scientific literature,” LeJeune explains. “The work looking at the effects of pasteurization that is published is subject to peer-review and unequivocally demonstrates that milk that has been pasteurized retains its valuable nutritional components.”

Contamination of unpasteurized milk

LeJeune and Rajala-Schultz’s paper indicates that the frequency of contamination in pooled farm milk has been reported to be <1% to 8.9% for Salmonella species, 2.7% to 6.5% for L. monocytogenes, <1% to 3.8% for Shiga toxin-producing E. coli, <1% to 12.3% for C. jejuni, and 1.2% to 6.1% for Yersinia enterocolitica.

These organisms are all in the dairy environment and therefore could end up in milk, because the farm and barn environment or milking procedures are not and never will be sterile or even aseptic. Possible contaminates, those responsible for spoilage and pathogens are widely distributed in the farm environment, LeJeune notes. As milk is excreted, it can become contaminated with bacteria that live as commensal microflora on the teat skin or on the epithelial lining of the teat canal. “It is not reasonable to think that every microscopic particle can be prevented from entering milk,” he says.

“We know for sure that E. coli, especially O157:H7, Salmonella as well as Listeria can cause severe disease in humans,” Rajala-Schultz says. “The connection between Mycobacterium avium subspecies paratuberculosis and human disease is still debated.”

Any organism that is acquired via ingestion could result in infection if it is present in milk, LeJeune adds. “In addition to the other common pathogens, Listeria has one of the highest case fatality rate of all foodborne diseases. These are all likely to be found in the dairy-farm environment.”

Coxiella burnetii, causative agent of Q fever, rarely causes clinical disease in cattle — it can be associated with reproductive problems and it is shed in high numbers in birth-related tissues and fluids of infected animals. Therefore, the most common route of transmission for Coxiella is through aerosols or direct contact with placenta, birthing fluids, etc. during calving, even though the organism can also be shed in milk and could be transmitted via ingestion of unpasteurized milk as well.

Contamination of milk can occur quite easily. “If and when the organisms are on the teat skin or in the teat canal  it is very easy for them to get into the milk during milking,” Rajala-Schultz says. “Even when people are trying to collect aseptic milk samples for mastitis diagnosis and the teats are dipped, wiped and stripped, the teat ends are scrubbed with 70% alcohol swabs and gloves are used, it is still possible to get contaminated samples if not paying attention to the sampling procedure. Milking hygiene is of extreme importance to ensure high quality milk.”

Microorganisms are capable of proliferating in milk. Thus even if they are excreted very low numbers, such as with a subclinical infection, they can proliferate at a later time, says LeJeune. “If milk is not cooled quick enough, this gives the bacteria an opportunity to multiply and even small initial amounts of any bacteria in milk can multiply exponentially quite quickly,” notes Rajala-Schultz.

Raw milk vs. raw colostrum

Some raw-milk advocates go a step further and seek out the most nutritious milk there is — colostrum —believing this “first milk” which is loaded with immunity factors for the calf, is also more nutritious for humans. However, raw colostrum may be a bigger danger than raw milk. “Both regular milk and colostrum are extremely good growth media for bacteria, with all the nutrients they contain,” Rajala-Schultz explains. “The bacteriological quality of either milk or colostrum is largely dependent on how the product is handled, how quickly it is cooled after collection, etc.”

Rajala-Schultz says based on a recent study from Pennsylvania, bacterial counts in raw colostrum were considerably higher than in raw bulk tank milk, as reported earlier in a separate study also from Pennsylvania. “I would speculate that the difference is likely due to the handling of colostrum as it may not get cooled down as quickly and efficiently as ‘regular’ milk, thus allowing more time for the bacteria to multiply.”

Who is at risk?

As with many diseases, the young, the old and the immune-compromised are at greatest risk. Numerous CDC case reports about illness associated with raw milk involve children who consumed the product. One CDC report indicates raw milk products accounted for 4% ofE. coli disease outbreaks during a 20-year period from 1982–2002. 2007 unpublished CDC data also indicates that from 1998 to May 2005, raw milk or raw milk products have been implicated in 45 foodborne illness outbreaks in the United States, accounting for more than 1,000 cases of illness.

Rajala-Schultz says that in most raw-milk associated outbreaks, the majority of the patients have been young children. “These kids are likely not capable of making informed decisions on this issue,” she says. “While I am sure that all parents want only the very best for their children, given all the knowledge and documentation we have about the potential disease risks related to raw milk, it is amazing that some people are willing to take that risk.”

 That’s what makes the practice of drinking raw milk so dangerous, agrees LeJeune. “It’s one thing for a consenting adult to engage in a dangerous practice after being informed of risks, but is it fair to children to expose them to hazards that risks are far higher and more severe risks without protecting them from uninformed or reckless adults?”

Communicating the risks

How veterinarians respond to questions about raw milk may depend on who is asking. Messages to farmers will be different than those to consumers, LeJeune says. “Since consumers may be turning to farmers for information and advice, especially with the explosion of community supported agriculture initiatives, producers need to be in the know of what the risks are for both their customers and for the health of their own families.” In addition, he says, physicians need to be alerted to the possibility of these disease showing up.

LeJeune believes redirecting the question may be a better way to get the message across. There is no doubt in the scientific community about the hazard of raw milk consumption. “The debate is more on the level of social governance and peoples’ freedom to choose even if they choose to make unwise decisions. A similar debate has been raging among people who do not wish to have their kids vaccinated against childhood diseases.”

“This may be a question about a freedom to choose and not being told by the government what one can and cannot eat,” says Rajala-Schultz. “The overall message, however, is that the disease risks with raw milk consumption are known and well-documented, and the consequences can be very serious. The barn environment is not sterile and numerous microorganisms are ubiquitous in the environment. It is impossible to produce milk without any bacteria in it.”

The dairy business is a hard business to succeed at financially. The lure of making more money for raw milk products may look attractive to some producers. However, the consequences can be high, according to LeJeune. “Not only is there the potential for legal action, loss of licenses and loss of revenue, but someone selling raw milk could ultimately be contributing to the loss of a life.” 

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