Now it's spontaneous

[Amelia]

Mystery US mad cow cases

June 13, 2006

WASHINGTON: A mysterious strain of mad cow disease that can appear spontaneously in cattle appears to be responsible for two cases in Texas and Alabama.

Government officials are trying to play down differences between the two cases and the mad cow epidemic that has led to the slaughter of thousands of cattle in Britain since the 1980s.

But it is these differences that are complicating efforts to understand the brain-wasting disorder, properly known as bovine spongiform encephalopathy, or BSE.

The cows in Texas and Alabama appear to have had an atypical strain that scientists are only now starting to identify. Such cases have been described in about a dozen cows in France, Italy and other European countries, as well as in Japan.

In the two US cases, researchers did not detect the telltale spongy lesions caused by prions, the misfolded proteins that deposit plaque on the brain and kill brain cells.

In addition, the prions in brain tissue samples from the Texas and Alabama cows seemed to be distributed differently from those that would be expected to be found in cows with the classic form.

French laboratory studies on mice showed that the classic and atypical strains could be spread from one animal to another. But scientists theorise the atypical strain might have infected cattle through an unusual way.

Mad cow disease is not transmitted from cow to cow like a cold or the flu. It is believed to spread through feed, when cows eat the contaminated tissue of other cattle. That happens when crushed cattle remains are added to feed as a protein source. This practice ended in the US in 1997.

Humans can get a deadly related disease, variant Creutzfeldt-Jakob disease, by eating meat contaminated with mad cow.