I guess they conceivably could but how do they contract it in the first place? Are there a large number of Liberia or Sierra Leone to Central America travelers?
If they want to get in the US w/o having to get visas, sure.
They’ve found all manner of OTM papers/documents/stuff on the border.
Well how about Boko Haram militants getting a couple dozen volunteers to be bio ‘bombs’ exposed placed on a plane to Mexico and then cross over? Pretty simple and cheap intercontinental weapon delivery systems wouldn’t you say?
It only takes one. Face it, no one knows who or what is coming across. It only takes one coming across the border, or on a plane or a ship.