AAMC FL 2 B/B Passage 8

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This whole passage just messed me up. I think it may be a gap in my content knowledge and I'm hoping someone can help me with it.

I'll try not to disclose too much but this sentence I can't seem to comprehend.

"The infectivity of VSV-EGP , vesicular stomatitis virus (VSV) particles engineered to contain EGP instead of VSV glycoprotein in the viral envelope, was reduced more than 99-fold by inhibitors of the mammalian proteases CatB and CatL. In a separate experiemnt using a strain of Ebola Virus, CatB inhibitors reduced the number of Ebola Virus particles produced in a cell culture 10 fold."

I understand the second sentence in relation to the first sentence. I understand (I think) that CatB and CatL are needed for the infection to occur but I don't know why inhibition of proteases, which break down proteins, would decrease infection. I would think the EGP protein (transmembrane viral glycoprotein) would be degraded by proteases which would make the virus not be able to incorporate its genome into the target cell and reduce infection?

Very confused specifically with that sentence. I was able to interpret the graph decently but having a hard time with some of the wording in here.

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