This 1997 article in Lancet takes a look at three cases of zombification in Haiti and attempts to explain them through medical science. It not only gives a clear description of the most common, local interpretations of the Zombie phenomenon but it also shows how mistaken identity and psychosis could cause people to be misidentified as Zombies.
While it doesn’t deny that datura and pufferfish poison could play a role in inducing a catatonic state, it presents the case that the sheer number of cases of zombification in Haiti and the ease in which locals will identify a person as a Zombie makes it difficult to attribute all the cases of zombification to a single cause.
In all likelihood, these cases of zombification represent a myriad of different sociological, psychological and physiological systems that are being convolved into a single cause.
For those of you seeking succor during the Zombie Apocalypse it is beginning to look like Haiti might not be quite as bad a place as we might have initially believed. With so many psuedo-Zombies ambling about, the walking damned might not consider it fertile hunting grounds.
That being the case, you will still want to stay out of the Eastern Bloc.