I think it’s reasonable he didn’t know she had Ebola while they were hauling her around the city in a taxi. Since she died before he left for America, it’s pretty unlikely he didn’t know before he left what she had died of and that he had probably been exposed.
I think it’s really interesting that the taxi driver is still alive to give interviews. He was presumably equally exposed but didn’t catch the disease.
Jimenez Grugbaye, the cabby who transported Duncan and his landlords and their desperately ill pregnant daughter, has reported that they denied in response to direct questions that she had Ebola. They insisted her condition was strictly related to pregnancy complications. The cabby said "I decided to ask him to intervene a bit as to regarding this sickness, what type of sickness it really was, and she told me and reassured me it was not the Ebola thing, it was like abortion."
It seems quite likely they told Duncan the same story. After all, their daughter was dying, and they needed to enlist muscle to seek help for her.
You can make the argument that Duncan should have known she had Ebola. After all, the cabby also reported that, after earning his fare and reflecting upon what he had seen, he was sufficiently alarmed that he fumigated his cab twice and visited a clinic to be checked.
However, the fact remains that Duncan did not object when, after his first ER visit in Dallas, he was sent on his way with a worse than useless antibiotic prescription. That argues that he didn't know how much trouble he was in. Or he was in a state of serious denial (Hey — I helped my landlord's daughter. She was a horrible mess, but it wasn't Ebola. And I was OK at the airport, and the Dallas docs didn't think my illness was a big deal even after I told them I was from West Africa. Whew! So far, so good!).
He'd procured his ticket and visa well in advance of his Ebola exposure. I think his plan was to convert his tourist visa into permanent US residency either by marrying his GF or simply overstaying his visa. Then Ebola hit him from left field.