Brain-punking Parasites

February 1st, 2007

A while ago I promised a slew of zombie-themed Awesome Science Videos, and that onslaught begins today. I’ve already posted an article featuring a fascinating, if disturbing, video detailing Soviet attempts at zombification (catchily titled “Experiments in the Revival of Organisms). Now it’s time to turn our attention to Mother Nature’s efforts, which are (as per usual) far more successful than our own clumsy attempts.

First up is the Gordian Worm, a small, thread-like creature that lives in freshwater environments, so named for its tendency to contort itself into intricate tangles akin to the mythical Gordian Knot. Growing to around 25cm long, but only 1mm wide, the adult worm leads an unremarkable life wallowing in mud. The juvenile, however, is a particularly nasty parasite that infects, digests, enslaves and finally kills its host.

When the tiny larvae hatch, they cannot survive long in the water and must find a host. Using an armature of spines on the proboscis, they bore into the flesh of whatever unfortunate animal happens to pass close enough. In fish, snails, crustaceans, the life cycle does not continue further. The Gordian Worm requires a terrestrial host, and to achieve that it will infect the larval stage of an insect such as a mosquito or dragonfly. When this insect metamorphoses into a flying adult, the dormant parasite is carried inside, surrounded by a protective cyst.

Should this host be eaten by another invertebrate, such as a spider, beetle or mantid, the Gordian worm begins the next stage of its gruesome life cycle. We’ll be looking at one particular species of Gordian worm, Spinochordodes tellinii, that infects crickets.

Once in the cricket’s gut, the cysts break open and the larva penetrates the gut of the host. Secured in place, it secretes digestive enzymes through its skin and begins to digest the living host. Over a number of weeks, the larva develops into an adult Gordian worm, all the time feeding on the cricket’s insides.

Once mature, S. tellinii needs to return to water to complete its life cycle. To do this, the Gordian worm infects the cricket’s mind, and forces it to commit suicide. Little is known about how the worm achieves this, but French scientists recently reported that the expression of certain proteins in the infected cricket’s brain were altered, namely those involved in neurotransmitter function and geotactic behaviour. The partly-digested and now zombified cricket seeks out water, and once there, throws itself in, and drowns. The adult Gordian worm then burrows out of the cricket carcass, swimming away to find a mate. So uninterested is the Gordian worm in the non-parasitic stage of its life cycle that it doesn’t even have a mouth – it will live on the reserves built up whilst inside the host and then die. Each female Gordian worm can lay up to 10 million eggs. Bad news for crickets, good news for zombie fans.

http://video.google.com/videoplay?docid=7226661303929118618

Entry Filed under: Awesome Science Videos

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