Parasites, and drugs that can cause someone to seem like a zombie. With all the craze being in zombie movies and games, many people question, can a zombie apocalypse actually occur?! Probably not, but the symptoms of a zombie could!
It is actually more probable for zombie-like symptoms, rather than the typical form of a zombie that is seen in movies and video games. However, you do have to minus the whole “transmitted by bite” factor.
If you have read “The Serpent and the Rainbow”, then you would know about Clairvius Narcisse.
He was declared deceased by two doctors in 1962, and found wandering around the village 18 years later after being determined deceased. In April 30th, 1962, Clairvius Narcisse was omitted to the Albert Schweitzer Hospital. On May 2nd of that year, he was pronounced dead by two attending physicians. The body was placed in cold storage for 20 hours, then taken for burial. On May 3rd he was then buried north of his village and ten days later his family placed a concrete slab over his grave. Eighteen years later this man approached his sister in their village, and introduced himself by a childhood nickname that only close family members would know(Davis).
It is said that this was common in Haiti at that time, people were being poisoned by a “sorcerer” with various drugs, and being forced to work on a sugar plantation. Poison from pufferfish was used to simulate death, and a paste made from Datura, which at certain doses has a hallucinogenic effect and can cause memory loss. With the combination of these two things, Clairvius Narcisse and many others were “zombified”. Many people were basically brain dead, being forced to work on this sugar plantation, had no idea who they were, or where they were. When the “sorcerer” finally died, and regular doses of the hallucinogen ceased Narcisse regained his memory, and sanity, many others however, did not.
You can look at a more thorough article about Clairvius Narcisse’s story here: http://www.biology-online.org/articles/dead_man_walking.html
Even parasites and diseases can cause zombie like symptoms, most of them are in bugs and insects though. Toxoplasmosa gondii is a parasite that controls the brain. It is found in rats, the parasite can only breed inside the intestines of a cat, so the parasite basically has to get the rat to the cat(Hokelek). There are other forms of this parasite though, such as an ant being driven to climb on the highest blade of grass to be eaten by a bird. These parasites just need a host, and they pretty much control them. Toxoplasmosa gondii seems like it would be a dangerous parasite on a large scale in humans, is it possible for it to cause a zombie? Probably not, but you never know.
It is also said when toxoplasmosis gondii is high in pregnant women, that the child has higher chance of developing schizophrenia. This parasite and schizophrenia are closely related. Who says that it can’t cause someone to go on some killing rampage.
So, zombies are very unlikely, but to get the symptoms you really just need someone who is brain dead, and aggressive. Really just trying to get the “what if” thought process going.