A mutation of swine flu has been detected in Brazil.
The Adolfo Lutz Bacteriological Institute says its researchers have identified and isolated a new strain of the H1N1 virus in a patient in Sao Paulo.
It is not yet known whether the variant is more aggressive than the more common type.
The institute says the mutation comprised alterations in the Hemagglutinin protein, which allows the virus to infect new hosts.
There are fears the virus could mutate into a more deadly form, as happened with the 1918 Spanish flu, which killed tens of millions.
While big pharmaceutical firms are ramping up efforts to mass-produce a vaccine for H1N1, they are still months away from having enough stocks - too late for the Southern Hemisphere's winter flu season.
South America has already recorded five deaths from the disease: two in Chile, one in Colombia last week and, most recently, those of a three-month-old girl and a 28-year-old man with leukemia in Argentina's capital Buenos Aires.