Mr. Duncan knew he was exposed to Ebola. The more interesting question is

[ecstatic]

41. It is suspicious, but if the NY Times article is true,

Mr. Duncan, the first person to develop symptoms outside Africa during the current epidemic, had direct contact with a woman stricken by Ebola on Sept. 15, just four days before he left Liberia for the United States, the woman’s parents and Mr. Duncan’s neighbors said.

http://www.nytimes.com/2014/10/02/world/africa/ebola-victim-texas-thomas-eric-duncan.html

Unless the 21 day incubation period is wrong, this guy quit his job before becoming infected. It's possible that he mistakenly thought he had already caught it and quit his job and purchased the flight to the US. That would explain his direct and prolonged encounter with his landlord's family (if he already thought he had it and was confident that he'd be cured in the US). Of course, that doesn't explain why he'd expose his wife and kids to the virus.

Alternatively, he exposed himself to the virus on purpose because he was fed up with seeing so many people dying--possibly in response to the meme about Ebola's cure being 50 white people away? That still doesn't explain exposing his family, unless he was aiming for an indirect murder-suicide (but was taken aback by how ill he became and decided to get care?). Or maybe he thought the whole family would be cured and it wouldn't be a big deal?