Canada's National Microbiology Laboratory reports that the virus is new; "about 80% of the virus is highly related to a North American body of swine flu that has been around for a number of years, but about 20% comes from an Eurasian variety of swine flu first seen in Thailand, so its recombined to create something totally new. How it did that, where it did it, when it did it, I don't think we know yet."
http://www.cbc.ca/health/story/2009/04/24/health-flu-mexico090424.html

Work at the U. S. CDC further elucidates that the N. Am. material is a combination of swine flu, avian influenza virus and human influenza virus.

Speaking today, a spokesman from the CDC said it is too early to tell if it originated in the U. S. or Mexico.

[? It could have spread in the Mexico City area because of the close concentration of people. The Thailand element also adds to the question of its origin.] Travelers are probably spreading the virus.

The WHO has stated that it is now a human virus. WHO also confirms that the virus has not affected the very old or the very young, this is unusual and causes concern.

Putting the outbreak in perspective, 4000 people die of flu virus each year in Canada alone; Canada's population is not much more than that of the Federal District of Mexico (Mexico City and immediate environs).