Zombies in nature

Haitian folklore tells of the zombie: a reanimated corpse. In modern day, the zombie is portrayed as parasitic, feeding on the brains of others and so infecting them

Zombie via Wikipedia Commons.

to become zombies too.

There are various parallels in nature: fungi that infect the brains of ants, the Euhaplorchis californiensis worm that infects fish, or the toxoplasma gondii parasite that infects rats (there’s more about toxoplasmosis here) – all these force their hosts to change their behaviour to help spread the fungal spores, or get themselves eaten by a bird or cat, where they can reproduce.

We don’t know how this happens, but researchers looking at some of these parasites found they excrete chemicals that alter brain chemistry. In their target host, the cocktail has a profound affect on behaviour, but doesn’t work so well in other species.

Toxoplasmosis (Things We Don’t Know about Pregnancy Series #6)

I once heard someone talking about arranging a hen do and struggling for ideas that would be okay for pregnant participants. At the time, I couldn’t see why it was so difficult… they were pregnant, not dead! …But I guess it depends how risk averse you are. If you’re avoid absolutely everything that could pose any tiny risk that includes alcohol, caffeine, household chemicals, saunas, certain foods, sports, paint, gardening, cats, non-stick frying pans and any person who could have an illness. In fact, staying locked indoors without human contact.

The outdoors thing intrigued me.

The great outdoors © TWDK.

So what is the risk?

Cat and mouse © TWDK.

The panic is over toxoplasma gondii, a protozoan parasite that will infect a third of people over their lifetimes. Most people never know: the zoonotic infection is asymptomatic in healthy adults, and humans are considered dead-end accidental hosts, because toxoplasma gondii can only reproduce in cats – and wants to get back in cats.