Could a brain parasite found in cats help soccer teams win at the World Cup?

The state of the universe.
July 1 2010 7:26 PM

Landon Donovan Needs a Cat

Could a brain parasite found in cats help soccer teams win at the World Cup?

Ghana player Kevin-Prince Boateng. Click image to expand.
Ghana player Kevin-Prince Boateng

What if I told you that last week I predicted all eight winners of a round of the World Cup? And that instead of rankings or divination all I did was look up how many people in each team's home country had a tiny parasite lurking in their amygdalas? Would you believe me? A decade ago, Discover Magazine concluded that parasites ruled the world, and now I'm going to try to tell you that, at the very least, parasites rule the World Cup.

First, a quick primer on the organism in question, a single-celled parasite called Toxoplasma gondii.

Toxo is one of the most successful parasites in the world and is found in almost every type of mammal. Goats, cows, pigs, sheep, humans. But it spends its time trying to get into the stomach of a cat, the only place where it can successfully reproduce. Thus the organism has evolved an unusual lifecycle relating to the brains of rats and mice. Rodents ingest little bits of Toxo from cat feces and Toxo goes straight to their heads.Once there, it scrambles the neurons around and reverses the animals' natural aversion to cat urine. Soon after, a recently relieved cat returns to the scene and takes its supper. In other words, the rat plays taxi to the parasite, finding it a new feline host and completing the Toxo lifecycle.

Advertisement

Livestock fields are full of fertilizer made from, you guessed it, bits of cat feces. When the cows and goats graze, they ingest Toxo, and it sneaks its way into their brains. Eat one of these livestock uncooked and you'll get Toxo in your brain, too. Thanks to the urbanization of cats (and their feces), almost a third of the human population now has a chronic, latent, and seemingly innocuous Toxo infection. This is, of course, an average: Rates vary a great deal from one country to another, from 6 percent in South Korea to 92 percent in Ghana.

A recent article in The Economist pushed the idea that Toxo infection can subtly influence human behavior and, writ large, worldwide culture. Studies find that national infection rates correlate with overall personality traits like neuroticism, perhaps because Toxo is having some effect on how our brains function. (According to one theory, the parasite can alter levels of dopamine, a neurotransmitter associated with reward and motivation.) But this research fails to consider one of the most compelling measures of national character: World Cup victories. Could rates of Toxo infection predict soccer success?

If we set aside the qualifying rounds (in which teams can play to a draw) and focus on matches with a clear winner, the results are very compelling. In the knockout round of this year's tournament, eight out of eight winners so far have been the teams whose countries had higher rates of Toxo infection. If we go back to the 2006 World Cup, seven out of eight knockout-round winners could be predicted by higher Toxo rates. The one exception to the rule was Brazil's defeat of Ghana, a match between two nations that each have very high rates. (Aside from having the winningest team in World Cup history, Brazil has quite a few cases of Toxo: Two out of three Brazilians are infected.)

It gets better. Rank the top 25 FIFA team countries by Toxo rate and you get, in order from the top: Brazil (67 percent), Argentina (52 percent), France (45 percent), Spain (44 percent), and Germany (43 percent). Collectively, these are the teams responsible for eight of the last 10 World Cup overall winners. Spain, the only one of the group never to have won a cup, is no subpar outlier—the Spaniards have the most World Cup victories of any perpetual runner-up. 

What is going on here? Does Toxo really make people better at soccer?

The relationship is neither linear nor foolproof. Italy managed to win the World Cup in 2006, despite its relatively average infection rate of 33 percent. Certain African countries plagued with public health problems have astronomical Toxo rates. Yet the heavily infected players of Ghana, Gabon (71 percent), and the Ivory Coast (60 percent) have not yet managed to win a single cup. On the other end, England (6 percent), the U.S. (12 percent), and Japan (6 percent) are pretty OK at soccer yet have some of the lowest rates in the world.

So what can we make of the statistics? It looks like having some Toxoplasma gondii in the collective brains of your home country makes your team a little bitbetter at soccer, so long as you're already among the top teams in the sport. Thus a difference in infection might separate a team like Germany (43 percent, three * World Cups) from perpetually lackluster England (6 percent, one World Cup).  And a bit of reflection reveals that the U.S. (12 percent) didn't stand a chance against Ghana (92 percent), neither in this tournament nor the last one.

Now, what does the Toxo parasite do that could possibly relate to soccer performance? Not much is known about its impact on the human brain, but there are clues. We know that infection increases testosterone in male brains, making them more likely to get into car accidents, more attractive to females, and more prone to being jealous, dogmatic, and dismissive of authority. Evidence even suggests that motorcyclists are more likely to have Toxo. Something like a James Dean effect. Generally, males with Toxo are more aggressive and less inhibited. Keep in mind that FIFA, in line with most sporting organizations in the world, bans testosterone supplements of any kind. But they do not ban Toxo, and if Toxo increases testosterone levels, we may be dealing with a form of inadvertent, cultural doping.

Certainly, there are caveats. First, it might be foolish to assume that the players on a national team will have the same rate of infection as their countrymen (especially if infection confers some kind of competitive advantage). On the other hand, having more Toxo-infected people around you at a young age might help your development as a player. Second, some studies have shown that those infected with Toxo have slower reaction times on certain tests than matched controls. It's not clear how or why that effect would be helpful to a soccer player—or indeed that it would be something other than a detriment. Finally, it's possible—likely, even—that the correlation between Toxo infection and World Cup success is a coincidence, or that it reflects some other common trait among successful soccer nations. Maybe it helps to have raw meat in your diet, and Toxo is just a side effect?

In any case, let's pause a moment before we start serving goat sushi at youth soccer camps. Prudence would say we wait until we know exactly how Toxo does what it does. Let's use what information we have in just the sensible and cautious way you might expect from a nation without Toxoplasma gondii or, coincidentally, a World Cup.

Correction, July 2, 2010:The original article assigned four World Cup trophies to Germany instead of three. (Return to the corrected sentence.)

Like Slateon Facebook. Follow Slate on Twitter.

Patrick House is a neuroscientist at Stanford University, studying Toxoplasma gondii.

  Slate Plus
Slate Picks
Dec. 19 2014 4:15 PM What Happened at Slate This Week? Staff writer Lily Hay Newman shares what stories intrigued her at the magazine this week.