Parasitic brainwashing and African sleeping sickness
The other day I was watching Smallville season 2 (hooray Netflix), and the next morning I read this story about parasitic hairworms “brainwashing” their grasshopper hosts, causing them to jump into water, effectively committing suicide. Anyway, the episode I was watching involved parasitic worms causing their human hosts to do crazy things. Go figure that I dismissed the idea as fun science fiction, only to read the next morning about the same thing happening in the insect world. (I shouldn’t have been surprised though, given the stupid things people do while cracked out on PCP.)
The parasitic Nematomorph hairworm (Spinochordodes tellinii) develops inside land-dwelling grasshoppers and crickets until the time comes for the worm to transform into an aquatic adult. Somehow mature hairworms brainwash their hosts into behaving in way they never usually would – causing them to seek out and plunge into water.
Once in the water the mature hairworms – which are three to four times longer that their hosts when extended – emerge and swim away to find a mate, leaving their host dead or dying in the water. David Biron, one of the study team at IRD in Montpellier, France, notes that other parasites can also manipulate their hosts’ behaviour: “‘Enslaver’ fungi make their insect hosts die perched in a position that favours the dispersal of spores by the wind, for example.”
Now scientists have worked out the mechanism by which these worms cause this mass suicide. The worms produce proteins which directly and indirectly affect the grasshopper’s central nervous system. (Video available; be warned, watching worms larger than their hosts look as though they’re being excreted from crickets and grasshoppers creeps me out.) While the explanation seems rather vague, it can be definitively be said that the grasshoppers and crickets and spiders are not in control of themselves when they take the plunge: they are not doing it willingly.
What’s even more interesting from a human point of view, is what this means for insect behavior and how it affects human beings. In the case of the Nematomorph worm, which starts out microscopic and grows to be larger than its host when it finally takes over, it causes the insect or spider to commit suicide. In the same vein, a parasitic organism like Trypanosoma may cause the host insect to have an increased appetite. This means that the vector — the tsetse fly in this case — may be more aggressive in feeding. This, in turn, can mean greater rates of infection because the odds of an infected tsetse fly biting are greater than those of a non-infected fly, which means more African sleeping sickness being spread.
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The “black spot” parasite which emmm.. cause black spots on fish, actually alter’s the behaviour of the fish causing them to swim closer to the surface of the water in order to get eaten by birds.
The reason for this is that the parasite actually breeds only in the stomach of birds. The offspring are passed (literally) by the bird back to water. The parasite then lives in snails, before returning to infect a fish.
An incredible journey.
Comment by Peter Gunn — February 18, 2006 @ 10:24 pm
but can they take over humans! I have a very good reason to beilive they do. help me. parisites. parisites.
Comment by none of your bissuness — December 15, 2007 @ 10:32 am