How I Learned to Stop Worrying and Love Toxoplasmosis
Last week, Carl Zimmer posted an excellent article on his excellent blog about the cognitive effects of toxoplasmosis in rats and humans. Toxoplasmosis (a.k.a. “litterbox disease”) is caused by a protozoan, Toxoplasma gondii, that lives in cats. According to recent research, the affliction apparently alters the behavior of infected rats and people. There’s no need to totally rehash Zimmer's well-written and thought-provoking post (you did read it, right?), but the lowdown is that hanging around cats can augment your social skills (if you're female), make you more territorial (if you're male), lower your reaction time and increase your risk for schizophrenia. Phew.
In the interest of full disclosure, I should reveal at this point that I am the proud owner of two cats.
I'm tired of seeing cats get kicked around. No pun intended – I've known far too many people perfectly willing to boot a cat across a room for next to no reason. And now, all those jackasses have Toxoplasma gondii as an excuse.
Naturally, I assumed Zimmer was a "dog person." Imagine my shock when I discovered he in fact owns a fine specimen of a cat named "Tino."
But before all you dog-lovers out there chortle and reach to pet your pooch, BEWARE! Having a cat would probably be safer. What parasite-host symbiosis could be more dangerous and destructive than a rabies-infected dog?
I kid, I kid... Cats can get rabies too, of course. It's just important to realize that despite the frantic and wild extrapolations people try to make from these toxoplasmosis findings ("CATS WILL DRIVE YOU CRAZY AND EAT YOUR SOUL," etc.), cats remain wonderful pets with well-documented health benefits. Owning and caring for a cat can make you mentally and physically healthier by decreasing your blood pressure, cholesterol and loneliness. Alright, alright, it's true; a pet dog can do the same thing. But do dogs hunt down and kill disease-carrying mice and rats? Nope. Not like cats.
Y'see, toxoplasmosis isn't that bad, really. You can make it work for you. Let’s run down the list:
- Infected women are slightly more outgoing and perhaps more promiscuous.
Sounds good – I'm all for it.
- Infected men display slightly more suspicion and jealousy.
Again, this isn't necessarily bad – for instance, being more suspicious can be useful if someone's trying to con you out of some money.
- Infection increases your risk for schizophrenia.
Well, this sounds bad. But there are lots of things out there that are known to increase schizophrenia risks, like living in a large urban area or being born in the winter or spring. Owning a cat probably carries as much schizophrenia risk as opening up the newspaper and reading Garfield.
Overall, it sounds like cats might be doing us a favor. Keep this privileged position in mind next time you're scooping out Kitty's litter box. Meanwhile, you dog-lovers might not have such an easy time with the deadly hantavirus you're liable to contract from an unchecked rodent infestation.
The notion that parasites can actually help host organisms seems pretty wild, but there's no reason I know of why this couldn't be abundantly true. After all, parasites are usually only noticed when they somehow damage their hosts. Does it stand to reason then that natural selection would favor parasites that actually benefited their hosts instead of being harmful or neutral? There's certainly room in the natural world for such creatures – according to some estimates, we have formally described and identified barely one percent of Earth’s microscopic organisms.
In a way, benefits from parasites aren’t really new – according to the Red Queen evolutionary theory, parasites are probably indirectly responsible for arguably humanity's most-adored activity: our habit of having sex to reproduce instead of using binary fission like amoebas. The idea is that the gene-swapping of sex keeps us one step ahead of our concurrently-evolving parasites, thus increasing our chances of survival. Though biologist Leigh van Valen first proposed this concept, science writer Matt Ridley popularized it and gave it a catchy moniker. The name references a character in Lewis Carroll's Through the Looking Glass who, though she eternally runs, always stays in the same place. Why Ridley didn't simply call it the "Treadmill" theory, I'll never know.



I'd like to make a preemptive correction to an article in the upcoming issue of the magazine. There's a piece in it on the attempts of several small biotech firms to introduce ex-Soviet bacteriophage therapies in the U.S. as an eventual answer to increasing rates of antibiotic resistance. 

It’s not over, of course, and never will be. We commend 


