a u.s. citizen from the middle east who died of variant creutzfeldt-jakob disease in texas in may 2014 likely ate contaminated uk meat .
investigators say the unnamed man , who was in his 40s , likely ate the tainted meat before moving to the u.s. in the 1990s .
variants creutzfeldt-jakob is a deadly neurological disease caused by abnormal proteins -- britain 's seen hundreds of cases since the 1990s .