Prions Suspected in Milk

[Guest guest]

Prions suspected in milk

Sheep mammaries shown to contain agents of fatal brain disease.

Andreas von Bubnoff

3 November 2005

Previously posted to SoFlaVegans list

 

http://www.nature.com/news/2005/051031/full/051031-7.html

 

Could sheep pass a fatal brain disease between them through their

milk?

 

The inflamed mammary glands of sheep have been found to contain

protein particles that cause scrapie, a sickness similar to mad cow

disease. This suggests that the suspect proteins, called prions, may

also be present in the milk of infected animals.

 

If prions exist in the milk of cows infected with both an

inflammatory illness and mad cow disease, formally known as bovine

spongiform encephalopathy (BSE), this raises concerns for human

health. Consumption of prion-contaminated meat from cows with BSE is

believed to cause the fatal variant Creutzfeldt-Jakob disease (vCJD)

in people; so might contaminated milk.

 

Adriano Aguzzi, the lead researcher on the study, has not detected

prions in milk itself, because it is difficult to analyse for the

abnormal proteins. But he says he expects to find them.

 

" It is unlikely that the prions are not in the milk, " says Aguzzi, a

pathologist at the University of Zurich Hospital, Switzerland. " And

the prospect is not a pleasant one. "

 

Neil Cashman, a prion researcher at the University of British

Columbia in Vancouver, is worried too. People have looked for prions

in the milk of cows with BSE and haven't found any, he says. " But

they haven't looked in cows with mammary-gland infection and BSE. "

 

" This raises very serious questions, " concludes Cashman.

 

Inflamed in the brain

 

Prions are mainly found in the brain, spinal cord and immune system.

Until recently, other body parts were thought to be relatively safe.

But in a series of studies, Aguzzi's group has shown that prions can

be present in other organs as well, provided that these organs are

inflamed.

 

Earlier this year, his group found prions in inflamed pancreases,

livers and kidneys. A study last month showed that the urine produced

by inflamed kidneys in mice also contains prions.

 

All this has helped to solve the mystery of how wild herds of elk and

deer, which are vegetarian, might manage to contract prion diseases

from each other. And it prompted Aguzzi to look at mammary glands to

see if they could carry prions too.

 

Viral culprit?

 

The researchers went to Sardinia, a Mediterranean island with more

than a million sheep, and analysed 261 sheep that were genetically

susceptible to scrapie. Of those, seven had scrapie, and four also

had an infection of their mammary glands. All these four had prions

in their mammary glands; the others did not. The study appears this

week in Nature Medicine1.

 

The mammary-gland infections were caused by a virus called Maedi

Visna. Aguzzi says that if this prion-virus combination is common, it

may be a clue to how to fight the transmission of scrapie. " Maybe to

eradicate scrapie you have to eradicate the virus first, " Aguzzi

says.

 

The prion concentration in the sheep's mammary glands is thousands of

times lower than in the brain, says Aguzzi. This is probably good

news, although it is not known how many prions it takes to cause vCJD

in humans.