New Zealand bio-security and food safety authorities this morning anounced the discovery of a disease in a single New Zealand sheep's brain, but were quick to emphasise that the discovery represented no trade or food safety risks.

The condition carries the names "atypical scrapie", and is otherwise known to scientists as "Nor 98". It is considered non-threatening.

The detection of the unfortunately named condition "does not change New Zealand's status as free from scrapie", BioSecurity New Zealand's principal international adviser Dr Stuart McDiarmid said.

"There is no evidence that atypical scrapie/Nor 98 can be transmitted naturally to other animals or to people, or that it in any way affects people."

There are no trade implications from the discovery.

Authorities were notifying the discovery in the interests of transparency rather than because of any regulatory obligation.

"There is no reason for people to change their eating habits or stop eating lamb or mutton and goat meat of products derived from these animals," the New Zealand Food Safety Authority's principal public health adviser, Dr Donald Campbell, said.

Most Scandinavian and EU countries, as well as the UK, USA and Canada had all detected the rare, non-contagious and spontaneously arising brain disease, which was found most often in older sheep.

"The widely accepted mainstream scientific advice is that it occurs spontaneously or naturally in very small numbers of older sheep in all sheep populations around the world," said Dr McDiarmid.

It had been expected to be only a matter of time before it was found in a New Zealand sheep, since "every country that has conducted sufficient surveillance for atypical scrapie/Nor 98 has found it in their flocks".

The current discovery occurred because New Zealand's scrapie-free status makes it a source of sheeps' brains used in testing for scrapie in other countries' flocks.

A single brain in a consignment of 200 to Europe for use in such tests was found to have the Nor 98 condition, so named because it was first identified in Norway in 1998.

The UK Spongiform Encephalopathy Advisory Committee has concluded that Nor 98 is a distinctively different condition from "classical scrapie" and may be more appropriately considered as a distinct condition "and not simply a variant of what is now called classical scrapie".