SAO PAULO - Brazil's Agriculture Ministry said on Friday that the country had registered no cases of mad cow disease, denying reports on some local media websites that said the disease had cropped up in the southern state of Parana two years ago.

In a statement on its website, the ministry said a cow that died in Parana in 2010 had tested positive for prions, the proteins believed to cause bovine spongiform encephalopathy, as the disease is formally called.

But the statement went on to say that the animal did not die of BSE and did not have symptoms of the disease.

"The World Animal Health Organization (OIE) in an official communication maintains the classification of Brazil as a country with insignificant risk of BSE," the statement said.

Share prices of Brazil's main beef companies sank in early trade after the reports 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 recovered half that slide after news of the government's denial began to spread.

Shares of beef producer Minerva SA fell 4 percent in early trade but later recovered half their losses. Marfrig Alimentos SA also recovered from early losses and was trading nearly flat with Thursday's close.

In 2010, the ministry had also denied reports of a case of mad cow disease after news agencies picked up on the story. The government said it would provide further details on the case later on Friday at a news conference.

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 a decade ago prompted beef importers to embargo shipments and caused temporary chaos in the industry. Brazil is the world's largest beef exporter.