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11 ways the world (as we know it) could end

By: Laura Moss on Feb. 16, 2011, 10:20 a.m.
zombies on Brooklyn Bridge

Photo: Seth Wenig/AP

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From annual zombie walks to popular TV shows like “The Walking Dead,” zombies have never been trendier. But could they be real? While dead humans can’t come back to life, certain viruses can induce aggressive, zombie-like behavior. For example, rabies, a virus that infects the central nervous system, can cause people to become extremely violent. Combine rabies with a flu-like virus that enables it to spread through the air, and you could have a “zombie” apocalypse on your hands. Scientists say a hybrid rabies-influenza virus is theoretically possible, but it would be difficult to engineer.

The existence of certain “mind-controlling” parasites is another common argument for the possibility of a zombie-like outbreak. For example, a parasite called Toxoplasma gondii is known to alter the brain activity of infected rats. This single-celled parasite lives in the guts of cats, shedding eggs that can be picked up by rats and other small mammals that cats eat. When a rat picks up such an egg, the parasite forms cysts in its brain that make the rat more likely to be eaten by a cat. How? Scientists discovered that infected rats no longer became anxious when they smelled a cat’s scent. In fact, the rats would explore the odor and return to the cat-scented spot repeatedly because its brain activity had changed. Infected humans have exhibited behavioral changes like slower reaction times and reckless behavior, and the parasite has also been linked to schizophrenia.