We all know that animals with rabies are nutty, aggressive, and prone to biting new victims. The rabies virus is transmitted to a new carrier whenever the mad sufferer attacks and bites somebody or thing. The new carrier then becomes nutty, aggressive, and prone to biting new victims. It’s a great strategy. I’d say that rabies, having been around since 2300 B.C., has had a good run with it. Unfortunately it is not the only parasite that changes its host’s behavior to accommodate a personal agenda.
Oliver Sacks in “The Man Who Mistook His Wife for a Hat,” describes a 90-year-old woman who lived for years quietly, modestly, contentedly. But then she started becoming excited, aroused by young men (70-year olds I’m guessing). She had an exuberance she hadn’t felt in years. Her friends worried. She was happier than ever, but also concerned. “Do you suppose it’s my old Cupid’s Disease acting up?” she asked Dr. Sacks. Turns out that that was exactly the case. She’d contracted syphilis in her wild youth and now, 70 years later, it was showing up again, changing her back into a carousing trouser chaser. Treponema pallidum is the bacteria behind syphilis–an STD. This little bacteria gets inside you and increases your sex drive. The more sex you have, the more Treponema you’ll spread around. Wicked smart strategy.
Beyond that the story is told of a fluke that lives in the liver of sheep. How the Lancet liver fluke winds up in the sheep is the fascinating part. It starts with snails crawling over the grass and consuming the feces of an infected sheep. Out of the feces hatch fluke larvae that turn into juvenile flukes which irritate the snails internals. The snails cough up the juveniles as if they were hair balls. When an ant slurps up the slime trail of an infected snail, it ingests the fluke balls as well. Once inside the ant, a liver fluke takes control of the ant’s mind and mandibles. It makes the ant migrate out of the ant colony up to the tops of the grass where it clamps onto a blade. Eventually a sheep will come along and ingest the ant and its juvenile fluke, thereby serving to incubate another generation of Lancet liver flukes.
Katie Selby of Eastern Michigan University, notes a weird twist to this plot. She says, “If [the ant is] not eaten, the fluke lets the ant loosen its hold on the grass and return to its daily tasks. This shows that the parasite has some sense of time because if it did not let the ant loosen its grip on the grass, the ant would sit all day in the sun, cooking … and killing itself in the process.”
Back in 2006, Peggy Kolm, posted on the subject of parasites changing behavior of hosts. She tells us: “Plasmodium, the cause of malaria, affects both its mosquito and animal hosts. Mosquitoes that drink plasmodium-infected blood initially become more cautious about finding another victim, giving plasmodium time to replicate. Once the plasmodium is infective, mosquitoes become more likely to bite more than one person in a night, and spend more time drinking blood.”
She also writes about Toxiplasma gondii. This is a protozoan that lives and reproduces in cats. Toxiplasma has a particularly nasty route to the cat’s gut. Rodents eat cat feces, so chances are a mouse will eventually come upon a pile of droppings from a cat infected with Toxiplasma. Here’s the mean part: Toxiplasma causes mice to lose their fear of cats. Once infected with a load of toxiplasma, a mouse will be easily caught and consumed by Kitty. Nice lifecycle.
Like the Lancet liver fluke, Toxiplasma has a weird twist in its plot: it can also wind up in humans and change their behavior. Let’s assume the feces winds up in a human because he or she handled a cat and accidentally ingested the toxiplasma, not because of some freakish behavior that had them actually…never mind. Anyway, as far as human behavior goes, Kolm suggests that there may be a “correlation between countries with a high rate of toxiplasma infection and increased neuroticism, uncertainty avoidance, and “masculine” sex roles.”
Thanks for reading.
Sue Lange’s latest ebook, Tritcheon Hash, is full of lapses of logic and weird science. “It’s a wild, good read.” Get your copy from Amazon or read a couple of free chapters at the publisher’s website.