Heroism: a viral infection?


We are just brushing the surface of ways in which viruses are able to manipulate the neurology and behaviour of their hosts. For a long time we thought of viruses and bacteria as simple disease vectors-parasites that hide within our bodies, until such time as they kill us or until our immune system routs them, but it seems that we have underestimated the sophistication of these microscopic invaders and the asymmetrical warfare they wage.

Toxoplasmosis Gandii is a good case in point. It is a protozoan parasite that has evolved to reproduce in a very specific environment - the digestive tract of cats. To arrive there, Toxo piggybacks within feline prey - rats, which in turn feed on cat faeces. This is in itself an elegant cycle; rats are eaten by cats and cats provide a food source for rats with the parasite being along for the ride as these two creatures perform their merry dance. However, Toxo is, it seems, far more than a passive stowaway.

Having migrated into the brain of the rat, the parasite works a subtle form of neurological witchcraft, which overrides the rodent’s fear response to the smell of their natural predators. Instead of being repelled by the stench of cats, Toxo-infected rats  seek out the source of the smell! Naturally, this perilous behaviour increases the chance that such rats will be eaten and so the parasite finds itself once again in the perfect environment to reproduce.

This fiendishly brilliant strategy has also been found to play out between chimpanzees and leopards, where Toxo also exerts its influence, and if apex big cats were running rampant in your city or town, you'd have good cause to be nervous because toxoplasmosis has also crossed over into human populations. Some estimates posit that up to 50% of us are hosts!

Now, here is where things get interesting - just because we are unlikely to become cat snacks, does not mean that we are unaffected by the behavioural manipulation Toxo exerts. Emerging research is irrefutable; toxin-infected humans are likely to undergo subtle personality changes which lead to a degree of disinhibition. Toxo dials down fear and increases the likelihood of reckless behaviour. Surgeons have now been instructed to test organs harvested from motorcycle accident victims, for example, because they are more likely to be toxic-infected than the average more conservative car driver. Toxo has also been connected to suicidal ideation and schizophrenia, but it is not simply an enslaving puppet master, hell-bent on destruction. 

Another way that the protozoa manipulates its host is by increasing the likelihood of successfully reproducing and then passing on its genes. A usually healthy animal has an innate aversion to potential sexual partners that are unhealthy or diseased. Toxo interferes with this pheromone pathway too, so that its host is perceived as more attractive to females (who are interestingly, otherwise less severely affected by the neuro-psychological effects of the parasite) and it is then passed through the sperm during sex. Remarkably then, Toxo can operate symbiotically as well as parasitically, bringing innate advantages to its host.

So there you have it. Toxoplasmosis Gandii-infected individuals are likely to be risk takers, are likely to break away from herd behaviours and perhaps are more charismatic than those who ‘choose' to play it safe.  Is it a coincidence that these are some of the same characteristics that underpin heroic behaviours? Could it be that the heroic impulse is, at least in part, a result of parasitic hijacking?

Just as we have come to appreciate that our gut biome is an ecosystem, the foreign entities within us influencing our appetites and urges, so too, it seems, we are riddled with viruses and bacteria which can modify our thoughts, feelings and actions. We may rationalise our behaviour, citing agency and free will, but we in truth, share the driving seat with other entities who have their own agenda.

It is perhaps a little premature to give Toxo a mask, a cape and to resign ourselves to side-kick status, but we might be on the cusp of a fascinating new field of study - heroism as a byproduct of neurobehavioral manipulation by outside vectors!

Andy Fisher