刚看到一篇，说H7N9不会让禽类致病，猪很有可能是中间宿主

也就是说，携带H7N9的禽类，看上去很健康没有生病，对大范围传播提供了方便。但如何会让人感染的，很可能有哺乳动物作为中间宿主，猪是一个重点怀疑对象。

http://news.yahoo.com/bird-flu-101-bad-h7n9-strain-093212234.html

引用几段：

Much still remains unknown about the virus, including how people are getting infected, but scientists say it contains genetic markers that could help it infect humans. It is circulating in poultry stocks, but is considered a "low pathogenic" virus that is not sickening birds. This can allow it to spread in flocks unnoticed, making it much harder to track and also possibly creating more contamination since the birds are surviving and spending more time on farms, in markets and elsewhere.

Although it is not yet clear, the virus appears to have mutated in a way that would make it easier for it to adapt and grow at normal body temperature in mammals. Scientists are working to figure out which species could now be playing host to the virus, and one possibility is pigs.

Swine are important because they share some basic biological similarities with humans, and they can serve as "mixing vessels" if infected with different flu strains at the same time.

"To me, the most important question to find out is: What is the actual host of this virus?" said Richard Webby, director of a WHO flu center at St. Jude Children's Research Hospital in Memphis, Tennessee. "It really looks like there's been some mammalian host involved."