SAO PAULO/PARIS, May 21 (Reuters) - Preliminary test

results indicate a commercial chicken farm in Brazil's state of

Tocantins is free from bird flu, a disease that can trigger

trade bans, according to a statement from the state's farm

agency on Wednesday sent in response to Reuters questions.

The initial test results are a boon to the world's top

chicken exporter, which is reeling from regional and countrywide

trade embargoes following confirmation of Brazil's first bird

flu outbreak on a commercial farm in the country's southernmost

state of Rio Grande do Sul.

A farm in Tocantins state and another in Santa Catarina

state have been under investigation for bird flu after

confirmation of that first outbreak.

The World Organisation for Animal Health on Wednesday

encouraged the use of zoning, a method focusing disease controls

on affected regions rather than the entire country, to contain

the spread of bird flu in Brazil and enable international trade.

Under WOAH rules, if a country detects a bird flu outbreak in

one region, it can declare that region a disease control zone

and maintain disease-free status - and trade - from other zones

that are unaffected.

Adapec, as the state's farm agency is known, said

authorities started the investigation on a local commercial

chicken farm after seven animals, out of about 40,000, presented

"torticollis" symptoms, the statement said.

"There was no high mortality among the flock, only the

culling of the seven animals for sample collection," the

statement said.

The agency said samples were taken from the animals and sent

to a federal laboratory in Sao Paulo immediately.

The Tocantins tests have indicated low pathogenicity, or

mild, influenza A. The samples tested negative for highly

pathogenic avian influenza - the type of bird flu that had been

spreading across U.S. dairy and poultry farms - and for

Newcastle Disease, which are the most worrying diseases in

birds, local authorities said.

Zoning was used by the United States after it discovered

bird flu outbreaks on farms, with countries like Canada, Mexico

and the European Union permitting imports from disease-free

regions within the U.S.

"This is particularly relevant because Brazil is a huge

country. As long as a country can guarantee that it is complying

with the rules, what is happening on one side of the country may

have no impact on the other side," WOAH Director General

Emmanuelle Soubeyran told Reuters in an interview.

A list from the ministry of agriculture still shows the

Tocantins commercial chicken farm as under investigation for a

potential bird flu outbreak. Another potential case of bird flu

on a commercial farm is under investigation in Santa Catarina

state, according to the updated ministry's list.

"Even with this reassuring initial result, the agriculture

ministry continues to carry out additional tests," Adapec said.

"This is a precautionary measure to rule out any risk and

guarantee health safety."