The farmer "may have exposed swine on the farm to an influenza virus, " said Dr. Brian Evans of the Canadian Food Inspection Agency.

CNN: Canada: Farmer possibly gave swine flu to pigs

The children were infected with a virus known as swine influenza A H1N1, which has a unique combination of genes not previously seen in flu viruses in either humans or swine - although it shares similarities with a virus that has been circulating in pigs since 1999.

CNN: CDC: Swine flu seen in 2 California children

The new virus has genes from North American swine influenza, avian influenza, human influenza and a form of swine influenza normally found in Asia and Europe, said Nancy Cox, chief of the CDC's Influenza Division.

CNN: Among the swine flu mysteries: Why only deaths in Mexico?

Already, some Southeastern states -- particularly Georgia, Alabama, Mississippi and Florida -- have been hit hard by the swine flu virus, also known as 2009 H1N1 influenza, perhaps because schools opened earlier there, she said.

CNN: Feds update H1N1 antivirals guidelines

Swine flu is a respiratory disease which is caused by a strain of the influenza type A virus known as H1N1.

BBC: India swine flu outbreak 'kills 94'

But the monitoring of birds, pigs, people and the genetics of the influenza virus have all been stepped up in response to recent outbreaks of both swine flu and bird flu.

BBC: La Nina 'linked' to flu pandemics