Herpes. The above article just leaves it up to your imagination, but as other articles point out "According to the CDC, this species commonly spreads herpes virus B through saliva, feces or urine."[1]
Which explains why she was given a rabies vaccine and treated with a course of Valacyclovir.
On a serious note, if the CDC told them to test for something, wouldn’t that answer the question about what the monkeys could have had?