BSE: How Risky is it to Drink Milk?

07/02/07 Prion proteins found in commercial milk. In a first-time global breakthrough, a Swiss start-up firm has succeeded in detecting prion proteins in the milk of humans, cows, sheep, and goats. This again raises the question of a "mad cow disease" risk from drinking milk. Tests are underway to verify disease-causing prions in milk.

Prions are known to be causes of neurological conditions such as Mad

Cow disease (BSE) and Creutzfeldt-Jakob disease in human beings. The causative agent destroys the central nervous system in humans and animals. It is known that prions can also emerge in body fluids such as blood and be transferred by them. In the past it was difficult to estimate the risk of an infection through blood transfusion or drinking milk, since the concentration of prions in body fluids is very low; nor is there a sensitive method to identify prions. Moreover, the incubation time for infection in human beings can take 10 years or longer.

Prion proteins in milk from the supermarket

From a consumer standpoint, milk and milk products were regarded as safe up till now. But this situation could change, since a team of scientists from the biotechnology firm Alicon AG, headquartered at Schlieren in Canton Zurich, has managed for the first time to detect prion proteins in the milk of human beings, cows, sheep, and goats. Using Alicon's new technology, prion proteins were even found in homogenized and pasteurized milk on supermarket shelves, as reported recently in the international science journal Public Library of Science (PLoS ONE).

In the case of the prion proteins detected, it is highly likely that they were of the normal variety posing no danger to health. However, the occurrence of the normal variety could mean that the milk of cows already infected with BSE also contains infectious prion proteins [i.e., prions] of the disease-causing variety. Alicon's head of research, Dr. Ralph Zahn, comments: "So far there has been no scientific basis for assuming that only 'healthy' prion proteins are present in milk and those causing disease were not."

Hence, beside blood and urine, milk is another body fluid in which prions causing disease could be present. As an American team of scientists has shown recently, infectious prions even arise in saliva.

Further research with infected animals

This finding coincides with a study conducted recently in this field by a Swiss prion researcher Adriano Aguzzi, an internationally recognized specialist. Aguzzi's research team at the University of Zurich showed that inflamed udder tissue found in sheep diseased with scrapie (a prion-induced ovine disease) actually contains infectious prions. The Alicon team is now continuing research work on the milk of infected animals. Research findings will show if milk is a potential carrier of BSE.

A possible answer to such a threat is introduction of a live BSE test and simultaneous scanning of dairy cows with BSE at an early stage. Alicon is offering the equipment needed for this. At present its team is working on completion of a rapid test to identify prions in milk and milk products.