As far as "leave of/leave from" goes "leave from" would be the better choice.
Finally the use of "enterovirus" is difficult to understand. This is not a name for a disease...rather this is a name for genus of (+)ssRNA viruses
Unless you are a specialist in this field of medicine there is no way for the reader of your sentence to understand what you are talking about. This word would appear only in a medical dictionary.
Use the KISS method (Keep It Simple Stupid) of writing sentences. Don't use $5 words that most people (including often the writer) don't understand unless they are necessary for clarity and you had an audience who understands them. It doesn't make the writer sound knowledgeable....it makes him sound ostentatious (to use a $5 word myself).
I would rewrite this
Melissa was under the weather because she was infected with a virus the other day; as a result, she left the party early without informing her host.