Okay, so when I say “zombies”, I’m thinking more zombie ants than shuffling, shambling, animated human corpses. But although you mightn’t think ants have much in the way of brains to start with, they have enough to be taken over and zombified by the fungus Ophiocordyceps unilateralis.
The fungus infects tropical carpenter ants (Camponotus leonardi), filling their bodies and heads, eating away muscles and destroying the central nervous system. The infected ants first wander randomly, then suffer convulsions that cause them to fall to the cooler, moister understory area, which is ideal for the fungus to grow and reproduce.
But wait, there’s more. At the height of noon, all the zombie ants bite the main vein on the undersides of leaves, and the muscles that control their mandibles detach so they lock in place and hang on, even after death. See Hughes DP, Andersen SB, Hywel-Jones NL, Himaman W, Billen J & Boomsma JJ 2011, “Behavioral mechanisms and morphological symptoms of zombie ants dying from fungal infection”, BioMed Central Ecology, vol. 11, no. 13, doi:10.1186/1472-6785-11-13.
Alright, but these are just insects; sophisticated mammals like ourselves are immune to microbial mind control, right?
Well now, it seems that rats infected by the single-celled organism Toxoplasma gondii develop a sudden, strange attraction for cat urine. Obviously, rats would normally be scared of that particular stench, but because Toxoplasma needs cats to reproduce, it seems to inhibit the rats’ defensive behaviour and stimulate their, ahem, sexual attraction.
For more on this, see House PK, Vyas A & Sapolsky R 2011, “Predator cat odors activate sexual arousal pathways in brains of Toxoplasma gondii infected rats”, PLoS ONE 6(8): e23277. doi:10.1371/journal.pone.0023277.
Toxoplasma can infect humans as well, but the good news is that it doesn’t take over our brains the way it does the rats’.
Even if it did though, it’s comforting to know that at least the US Centre for Disease Control is prepared for the zombie apocalypse.