For some reason, I’ve recently developed a morbid fascination with parasites. It started off a few weeks ago when I was listening to NPR and they had an expert on the show that mentioned Toxoplasma gondii, which needs to live in cat intestines to reproduce, but gets there by infecting rats. The expert mentioned that Toxoplasma makes the rats not fear the smell of cats, but that is something of an understatement. After a bit of research, I’ve found that it does that, and sometimes even makes the rats attracted to the smell, but it also makes them less averse to risk in general, slows their response times, and shortens their attention span. Recipe for cat food.
Well, it turns out that Toxoplasma gondii isn’t restricted to living in rats and cats, but can infect pretty much any mammal. Acute toxoplasmosis, the first phase of the infection, is only a problem in humans if the person has an immunodeficiency or is pregnant, in which case it can cause brain damage in the fetus, or possibly miscarriage (this is why pregnant women shouldn’t deal with cat litter). Traditionally, latent toxoplasmosis (the latter phase where Toxoplasma is basically dormant) has not been considered to be a problem in humans. That is, until researchers said “Hey, human brains aren’t all that different from rat brains”. This, coupled with the fact that 30-60% of humans test positive for toxoplasma antibodies, made them truly interested in it’s affects on humans. Much of the results are preliminary, but here goes:
Infected men tend to be more independent “rule breakers”. Infected women tend to be more conservative. In both, attention span and reaction times are worse than in the uninfected. You are more likely to be involved in an auto accident that is at least partially your fault if you test positive for Toxoplasma. Schizophrenics are more likely to be cat owners, and to have latent toxoplasmosis, but no study that I could find conclusively linked them.
That’s the weirdest stuff I’ve found involving humans so far, but there’s plenty of stuff going on in other species. A lot of the stuff I’ve found involves blood flukes. There’s one (Euhaplorchis californiensis) that reproduces in birds, but migrates through snails (that eat the birds’ droppings), through the water to fish, which they infect by swimming into the gills, finding a blood vessel, and then a nerve, ending up on the surface of the brain. The fish become more likely to jump out of the water or splash near the surface, which makes them about 30 times more likely to be eaten by birds, thus completing the fluke’s life cycle. The odd thing here is that it might actually be beneficial to the birds, since it makes getting food so easy.
Then there’s Dicrocoelium dendriticum, a fluke that reproduces in cows. Snails eat the manure, get infected and start shedding balls of slime with the flukes imbeded in them. Ants eat these balls, and then, every evening, climb a tail blade of grass and clamp onto the top with their jaws. In the morning, if they haven’t been eaten by a cow, they climb back down and behave like normal ants until the next evening. If they stayed on the blade of grass during the day, the sun would bake them and the flukes they carry.
By far the creepiest thing I’ve encountered, though, is Sacculina Carcini, a barnacle that infects crabs. The female will drill a hole in the crab’s leg, and inject an amoeba like clump of several cells. The rest of the female then dies. The blob swims around inside the crab until it finds the belly. Now the creepy stuff starts. Tendrils grow out from the barnacle, eventually infesting the entire crab, which stops growing and becomes sterile, but tends to live longer than average. If the crab is male, it becomes feminized so that it can house the barnacle’s egg sac, which ends up where the crab’s egg sac would be if it could still have one. The barnacle drills little holes in the crab’s body so males can get in to fertilize the eggs. Other than the fact that it has become a soulless hulk that only does the barnacle’s bidding, it behaves a lot like any other crab would, even cleaning the egg sac as if it was it’s own.
In any event, lots of things are living in you right now. Just hope that you, or whatever is left of you, still has the upper hand.
