First, somebody from Liberia probably isn't infected. As bad as things are over there, it's still <1% of the population. (For now.) Second, if they're well eno

First, somebody from Liberia probably isn't infected. As bad as things are over there, it's still <1% of the population. (For now.) Second, if they're well enough to be on the plane, even if they're infected, they're probably not going to be spreading that infection. By the time an ebola patient becomes contagious, they're usually not well enough to travel. And on top of all that, if they're actually contagious, I'd be worried about fomites generated while they're vomiting. Which they'd be doing in the lavatory. So in the general case, I don't think I'd be too worried about sitting next to them. (And if they're actually sick enough to be vomiting, I'd recommend being somewhere other than the lavatory.)