Two patients who recently arrived in Brazil from African countries have been put in isolation after showing symptoms linked to Ebola, officials said, raising concerns about the deadly virus spreading beyond the African continent.

A 37-year-old man who recently traveled to the Democratic Republic of Congo (DRC), where the outbreak has been concentrated, "exhibited symptoms such as fever, meeting the definition of a suspected case" of Ebola, the Sao Paulo state government said in a statement on Saturday.

The man was placed in isolation at the Emilio Ribas Institute of Infectious Diseases in Sao Paulo.

The patient was diagnosed with a severe form of meningitis and more tests were being conducted to screen for Ebola, officials added Sunday.

Another man was placed in isolation in Rio de Janeiro after arriving from Uganda on May 22 and showing "viral symptoms such as cough, chills and diarrhea," local officials said.

Rio City Hall told AFP on Sunday that the man had tested positive for malaria, but that the "case remained under investigation."

There have been more than 1,000 suspected cases of Ebola in the DRC since the outbreak was declared on May 15, including nearly 250 deaths, the Africa Centres for Disease Control and Prevention said on Thursday.

Several infections and one death have been confirmed in neighboring Uganda.

However, the true reach of the outbreak in the DRC, which is thought to have been circulating before it was detected, is likely to be much wider, the World Health Organization has warned.

The Sao Paulo government said that despite the suspected case, "the technical assessment indicates that the risk of the disease being introduced into Brazil and South America remains very low."