We all know the sources of colds and flus are viruses, which hijack cellular machinery to manufacture more viruses, which go on to infect more cells. Pretty straightforward, Watson/Crick stuff, right? Not entirely. Two scientists recently surmised that the flu virus might actually boost our impulse to socialize. The reason being is that the bug spreads through close physical contact and needs to find new hosts, fast.
Colorado State University parasitologist Janice Moore and Chris Reiber, a biomedical anthropologist at Binghamton University in New York, followed up on 36 subjects who received a flu vaccine. They knew the subjects’ immune system would react as if they had been hit by the live pathogen because the vaccine contains many of the same molecular components as the live virus.
The two discovered that the flu shot nearly doubled the number of people the subjects encountered during the brief period when the virus would be at its peak of contagion. “People who had very limited or simple social lives were suddenly deciding that they needed to go out to bars or parties or invite a bunch of people over,” Reiber told journalist Kathleen McAuliffe in a report for The Atlantic magazine.
Not a bad trick for a brief stretch of nucleic acid in a protein jacket, the code equivalent of a floppy disk. Yet a pattern of infectious persuasion goes on all the time in nature. There are tiny organisms that increase their chances of survival by turning their hosts into actual zombies. One such case involves the giant forest ant of Malaysia – Camponotus gigas to be precise.
If the insect is unlucky enough to breathe in a spore from a species of Cordyceptus fungus, its behaviour begins to change. For the first time in its life and completely against character, the ant leaves the forest floor to clamber up a tree. When it gets to the highest point, it freezes into position on a twig or leaf, sinks in its mandibles, and dies.
Having altered the ant’s brain prior to death, the fungus then devours the rest of the ant’s innards and within a few weeks, a mushroom grows from the head of the insect. More caps may develop from spikes growing through its exoskeleton. They eventually burst, releasing tiny capsules into the air.
According to the journal Nature Malaysiana, “these capsules in turn explode as they float downwards, spraying spores over the surrounding area and infecting unwary and unlucky insects. _ The life cycle of the fungus is thus completed.”
Here’s another zombie. The free-swimming larva of the Sacculina barnacle injects a few cells into the chink in a crab’s armour, which then grow into a network of filaments on the crab’s underside. The hapless host ends up being the crustacean equivalent of an Imperial Walker from Star Wars. Parasites such as Sacculina “control their hosts, becoming in effect their new brain, and turning them into new creatures,” observes science writer Carl Zimmer in his excellent study, Parasite Rex. “It is as if the host itself is simply a puppet, and the parasite is the hand inside.”
Ants and crabs may seem like little Darwinian wind-up toys, and we don’t have much problem thinking of their tiny brains and simple routines being tweaked by parasites – even if the molecular mechanisms still elude scientists. But how can the influenza virus – a thing so simple it exists on the border between life and non-life – nudge the neural pathways or neurochemicals of humans in such a finely tuned way?
It’s a mystery how we can be motivated to bust a move to the bar or bistro by an infectious agent that is millions of times smaller than the period at the end of this sentence. It calls into the question the very idea of human free will.
As science writer McAuliffe notes in her article for The Atlantic, with all those infectious agents “out there that may also be playing tricks on our minds – can anyone really know who’s running the show?” Considering that some scientists believe that up to thirty per cent of the human genome originated from viruses, I think I can answer that.