Brazilian officials said the animal that died in Parana in December 2010 did not have bovine spongiform encephalopathy (BSE), commonly called mad cow disease, just the protein believed to cause the disease, which likely appeared after a spontaneous genetic mutation in the 13-year-old cow.

Test results suggested the animal would have been unlikely to go on to develop the disease had it not died of other causes, the agriculture ministry said, adding the simple presence of the protein, called a prion, is considered an atypical case of BSE.

Results of tests carried out in England this month by the World Animal Health Organization (OIE) on tissue from the cow, confirmed the presence of the protein, Brazilian officials said in a press conference.

The OIE has not yet made its report public.

"The animal in question didn't manifest the disease and didn't die of this cause," said Executive Secretary Jose Carlos Vaz, one of the agriculture ministry's top officials.

Officials could not confirm the exact cause of death of the pasture-fed female used for breeding purposes, but said it had septicemia and mineral deficiencies. Its keepers notified authorities after it was found collapsed on the ground. It died 24 hours later. A neurodegenerative disease would have taken much longer to cause death, officials pointed out.

The OIE has maintained Brazil's status as a country with an insignificant risk of BSE, the officials said, adding Brazil would pursue legal action if necessary against any importer trying to exploit BSE claims to block imports of Brazilian beef.

Asked why it had taken two years for Brazil to send a sample of the cow's tissue to the OIE for testing on December 1, officials said the country adhered to the established protocol of conducting exhaustive tests at home first.

Share prices of Brazil's main beef companies sank in early trade after the media reports describing the case as mad cow disease were picked up and circulated by local equities analysts. Shares of Brazil's JBS SA slipped as much as 3 percent in early trade but later were down just 0.54 percent after the government published a denial of the reports.

Alexandre Inacio, an adviser for JBS SA, the world's largest beef producer, said the company had little to add beyond the ministry's statements.

Shares of beef producer Minerva SA fell 4 percent in early trade but were down just 0.45 percent in the afternoon as the Bovespa index rose 1.19 percent. Marfrig Alimentos SA was down 0.71 percent.

Marfrig said in an e-mailed statement that there are no incidents of mad cow in Brazil.

"The disease is related to the cattle's ingestion of animal products, which is forbidden in Brazil," the statement said.

The ministry had already denied reports of a case of mad cow disease after news agencies picked up on the story originally reported after the animal's death in 2010.

A story posted on the website of financial newspaper Valor Economico early on Friday said the cow in Parana had probably died of mad cow disease.

The outbreak of mad cow disease in Europe, North America and Japan over the past decade often prompted beef importers to embargo shipments and caused temporary chaos in the industry. Brazil is the world's largest beef exporter.

(Reporting by Reese Ewing, Caroline Stauffer, Gustavo Bonato and Peter Murphy; Editing by Lisa Von Ahn, Gerald E. McCormick and Bob Burgdorfer)

• A Permanent Economic Emergency