We all know what vampires are. Some of you may even think that such things are real. Well, they are. Not in the sense of actually having the dude with the teeth show up and ask to be invited in, but in the more insidious sense of having one take your soul. This, to me, is the real scary part of the fantasy, that your mind, your will, your identity could be devoured by a process that is sometimes represented as magical and sometimes (especially in the more modern era) as viral. That said, the supposedly more realistic biological transformations often move with ludicrous rapidity, ala the gory scene in Daybreakers where the vampire police goons turn on one another as they are progressively cured of the virus.

But in musing about the fantasy, one can’t but help to feel that there is an atavistic, visceral recognition of reality that should be respected. Because we can be taken over, mind and body, by viruses. The most obvious example is rabies, which slowly climbs the neurons into your brain, and then brings on a variety of behavioral changes, the most obvious of which is hypersensitivity and hyperaggresion (it is not for nothing that ‘rabies’ is the Latin word for ‘madness’). Think Cujo. Or, for a human version, Hap and Leonard encounter a rabies victim and foe in Lansdale’s brilliant “Bad Chili.”

Actually, now that I think about it, it’s a bit surprising that there aren’t more viruses that move their victims to do things they wouldn’t normally do, whether it’s open the window with someone floating outside (never open the window!) or irrationally bite anything that moves.

Or maybe there are.

My good friend Chris Sullivan, consummate virologist, loves to keep track of idiosyncracies of viruses. They are his friends, each one a personality to be savored. And so it was Chris who turned me on to the ‘zombie virus’ that takes over the brains of its caterpillar hosts (yes, I know, this is about vampires, but zombies are vampires with brains, until they don’t have brains, if you see what I mean; http://news.nationalgeographic.com/news/2011/09/110908-zombie-virus-caterpillars-science-weird-animals/). Once infected by a particular baculovirus, gypsy moth caterpillars climb high into trees, disintegrate as the virus eats them from the inside out, and then all the viruses ooze out of the remaining caterpillar muck and fall on their unsuspecting victims in the foliage below. The caterpillar’s brain was driven to this action, much as Cujo was driven to biting and Dracula was driven to overly dramatic entrances, by a viral gene known as egt.

Now, this is very cool: a single gene, that can promote a single action (climb tree, don’t stop until you reach the top). Who would have thought that behavior could be so … programmed. Well, biologists, really. Or at least the ones that know about behavior, instead of molecules (molecules are my friends). A really, really big snail, the Cone Snail, has developed a harpoon that it shoots into the much faster fish around it, paralyzing them and allowing them to be slowly devoured. The toxin contains a variety of peptides that interact with specific receptors in the brain. When injected into mouse brains, the toxins caused mice to “either jump, sleep, scratch, drag their hind legs, swing their heads or shake (http://www.accessexcellence.org/RC/AB/BA/pain_Meds/pain6.php).” Whoa.

But back to viruses. Again, there should be lots of possibilities for little things (viruses) to redirect the behaviors of big things (us), to their advantage. Chris recently pointed me to another example, this time with the somewhat well-known dengue virus, an insidious tropical disease transmitted by mosquitoes. Researchers at Johns Hopkins recently dissected the impact of dengue virus infection on gene expression in the mosquito, and found that there were changes in the production of numerous proteins. Amongst these proteins, though, were ones that “appeared to make the antennae more sensitive to odors — making them better at hunting humans, the virus’s only known mammalian host. Other changes in salivary gland genes appeared to make it easier for the virus to get into a mosquito’s saliva, ready for injection.” The virus turns the mosquito into a hunter-killer machine for the virus. If Japanese mosquitoes have anime, then there must be some awesome cartoons of the virus piloting a great big Gundam mosquito.

So, what does this mean for the future? Will viruses be engineered to take over our brains, turning us into foppish Victorians with capes and teeth? Um, unlikely. But the notion that there are more subtle behaviors being influenced by the genes of pathogens and other riders, that has legs. As more and more sequence data is collected from the bacteria that inhabit our gut (there’s more bacterial DNA in us than ‘us’ DNA), it’s becoming increasingly clear that not all the genes are just about making the bacteria happy to eat the stuff we put down our gullets, nor even just for the internecine bacterial warfare that goes on inside us every day in every way. No, the bacteria may be harboring genes that … guide us. It’s becoming pretty clear that there are bacteria associated with obesity, bacteria associated with diabetes, bacteria associated with schizophrenia …. But is this cause or effect? Do they inhabit niches that we’ve carved out for them, or did they do some of the carving? Who knows, although one recent study showed that bacteria-free mice have profound neurochemical changes, and much less anxiety (Neurogastroenterol Motil (2011), 23:255). And maybe there are genes like egt waiting to be found, genes that drive us to climb our own trees, or at least our own walls, all to the bacteria’s benefit.

- originally posted on Friday, April 20th, 2012