Whenever you use a past participle (such as "threatened" or "surprised") as an adjective, you create an unspoken subject. For example, if you say
"There is a buried treasure under the tree"
then the person who buried the treasure becomes an unspoken subject. "By" reveals that unspoken subject:
"There is a treasure buried by Bill under the tree."
You can also use "with". However, the meaning might change radically:
"There is a treasure buried with Bill under the tree"
has two possible meanings. On the one hand, it could mean that Bill was present when the treasure was buried. Unfortunately, it could also mean that Bill and the treasure are buried together under the tree.
"Threatened with tuberculosis" and "surprised with this" are valid expressions. The use of "with" does not make explicit that "tuberculosis" and "this" are the causes of the threat and the surprise, although this might be inferred. Sometimes, however, that inference might be false:
"The man came home to an incredible meal his wife had prepared for him. Never had he eaten such an amazing meal. He was also tired after a difficult day at work. He was surprised with time to rest at last."