I read on a thread a few weeks ago that it was suspected to be a variation of an avian (bird) strain, and ducks (seriously) were being looked at.
Apparently the markets in these Asian countries lack for hygeine, and carcasses are carelessly laid about...
Here's an article that suggests a bovine virus.
Virus may have crossed species barrier [ SARS ]
The deadly respiratory ailment SARS may have spread to humans from cattle.... some researchers say looks remarkably like bovine coronavirus. In cattle, the common disease is known as "shipping fever."