what's the difference between "look to something as ' and "look upon something as"

[chance22]

In a piece of news, it is said that: The new study may encourage people to look to viruses as a factor contributing to obesity.
I was told that look to can not be replaced by look upon, which I assume means "regard something as something". I don't know the difference between these two expressions. Could you explain it to me? Thanks.

[billmcd]

In a piece of news, it is said that: The new study may encourage people to look to viruses as a factor contributing to obesity.
I was told that look to can not be replaced by look upon, which I assume means "regard something as something". I don't know the difference between these two expressions. Could you explain it to me? Thanks.

I wouldn't consider use of "look upon" as necessarily wrong, but for me and in you example, it is a less emphatic term than "look to".

[chance22]

I wouldn't consider use of "look upon" as necessarily wrong, but for me and in you example, it is a less emphatic term than "look to".

Then are they of the same meaning, that is, look to here also means consider, but with emphasis? I found in the dictionary look to also means hope.