Even before this study, scientists had already suspected that a bacterium that has been tolerated for so long cannot be only bad. They had shown in experiments with mice that the H. pylori bacterium provides a reliable protection against childhood asthma. When the mice were given antibiotics, this protection disappeared and the infant rodents stood a chance of developing asthma again. When the bacterium was given to adult mice, the protective effect was still present but much less pronounced. You might say mice are not people, but this observation fits very well with the general trend noticed in industrialized countries in particular. Rates of asthma, allergies, diabetes, and neurodermatitis have risen as rates of H. pylori have fallen. This observation is far from constituting proof that H. pylori is the sole protection against asthma, but it may be part of the overall picture.
The theory suggested to explain this correlation is that this bacterium teaches our immune system to stay cool. H. pylori latches onto our stomach cells and by doing so causes large numbers of regulatory T-cells to be produced. Regulatory T-cells are immune cells whose job is to place a calming hand on the shoulder of the immune system when it flies off the handle like a drunk in a crowded nightclub. The T-cells say to the immune system, “Let us deal with this, mate.” As the name implies, these cells regulate the immune system’s reactions.
While the irate immune system is still shouting, “Get out of my lungs you bloody pollen-thing!” and showing its readiness to fight by giving us swollen, red eyes and a runny nose, the regulatory T-cells say, “Oh come on, immune system, that was a bit of an overreaction. The pollen-thing is only looking for a flower to pollinate. It’s just landed here by mistake. That’s more of a problem for the pollen grain than for us. It will never find its flower now.” The more of these sensible cells there are at work, the more chill the immune system will be.
When H. pylori causes a particularly large number of these cells to be produced by one mouse, another mouse’s asthma can be improved simply by transplanting those cells to it. That must be an easier solution than training a mouse to use a tiny little inhaler!
The incidence of eczema seems to be reduced by about one-third in people who harbor H. pylori. Increases in inflammatory gut disease, autoimmune problems, and chronic inflammations may also be a modern trend caused by the fact that we often unwittingly wipe out something that has protected us for millennia.
H. pylori Is Good and Bad
H. pylori ARE bacteria with many capabilities. They can’t be labeled simply good or bad. It always depends on what exactly the bacterium does inside us. Is it manufacturing dangerous toxins, or is it interacting with our body to protect it in some way? Are our cells constantly irritated, or can we produce enough gastric mucus for both its needs and our own? What part is played by agents that irritate the stomach’s mucus membrane, such as painkillers, cigarette smoke, alcohol, coffee, and stress? Is it a combination of all these that is responsible for stomach ulcers—because our little pets don’t like them?
The World Health Organization recommends people with stomach problems should get rid of the potential culprits. If stomach cancer, certain lymphomas, or Parkinson’s disease run in the family, it is also a good idea to offload H. pylori.
Thor Heyerdahl died in Italy in 2003 at the age of eighty-eight. Had he lived just a couple of years longer, he would have seen his theory about the colonization of Polynesia confirmed by studies of H. pylori strains. Asian strains of H. pylori conquered the New World in two waves, via the Southeast Asian route. But his theory about South American origins has not yet been proven. Who knows what bacteria still remain to be discovered before Heyerdahl’s theory is confirmed by a microbiological voyage of discovery?
Toxoplasmata—Fearless Cat Riders
A THIRTY-TWO-YEAR-OLD WOMAN cuts her wrists with a razor blade from the discount drugstore. It’s the thrill that makes her do it.
A fifteen-year-old racing-car fan crashes into a tree at full tilt. And dies.
A rat drapes itself over the cat’s food dish in the kitchen, presenting itself as a delicious meal.
What do these three have in common?
They are all failing to heed the internal signals that aim to preserve the huge community of cells that makes up living creatures. This community only wants the best for us. These three individuals seem to be pursuing interests at odds with those of their body—interests that may well have come out of a cat’s gut.
Cat’s guts are the home of Toxoplasma gondii. These tiny little organisms consist of only one cell, but they are counted as animals. They carry much more complex genetic information than bacteria. Their cell walls are also constructed differently and they probably lead more exciting lives.
Toxoplasmata reproduce in the guts of cats. The cat acts as their definitive host and all the other animals that toxoplasmata use temporarily as taxis to take them from cat to cat are defined as intermediate hosts. A cat can get toxoplasmata only once in its life, and the cat is a danger to people only during that time of infection. Most older cats already have their toxoplasmata infection behind them and so cannot harm us anymore. During a fresh infection, toxoplasmata are found in the animal’s feces. They mature in the cat litter for about two days before they are ready to infect their next host. If no cat happens to pass by but a dutiful, cat-owning mammal comes and cleans the litter, these tiny protozoa seize the opportunity. The microscopic creatures in the cat’s feces can wait up to five years to infect another definitive host. Their intermediate host does not necessarily have to be a human cat-lover. Cats and other animals roam through gardens and vegetable patches and sometimes get killed. One of the main vectors of toxoplasma infection is raw food. The probability, in percent, of your having toxoplasmata yourself is about as high as your age in years. On a global scale, about one-third of humans harbor them.
Toxoplasma gondii are counted as parasites because they cannot live on just any little patch of earth and absorb water and plant tissue—they need a little patch of organism to live on. As humans, we call such creatures parasites because we get nothing in return. At least, nothing positive, like monthly rent or affection. Quite the opposite, in fact—some can harm us by means of a kind of human pollution.
They do not have any overly negative effects on healthy adult hosts. Some people have mild, flu-like symptoms, but most notice nothing. After the acute infection phase, the toxoplasmata move into tiny apartments in our tissue and enter a kind of hibernation state. They will never leave us for the rest of our lives, but they are quiet little lodgers. Once we have been through this, we can never be reinfected. We are already occupied, so to speak.
However, an infection like this can have drastic consequences for pregnant women. The parasites can reach an unborn child via the mother’s bloodstream. The immune system is not yet familiar with them and is not fast enough to catch them. This does not necessarily always happen, but when it does, it can cause serious damage and even a miscarriage. If the infection is detected early enough, it can be treated with medication. But the chances of that are slim, since most people do not notice when they become infected. And in many countries, for example, a toxoplasma scan is not part of the standard set of pregnancy examinations. If your gynecologist starts asking strange questions like “Do you own a cat?” at your initial pregnancy examination, don’t brush the question off as meaningless small talk—she’s clearly an expert in her field.
Toxoplasmata are the reason your cat’s litter should be changed every day if there is a pregnant woman in the house (but not by her!), why raw food should be avoided by mothers-to-be, and why fruit and vegetables should always be washed. Toxoplasmata cannot be transferred from person to person. Infection can only come from the little residents of a freshly infected cat’s gut. But, as mentioned earlier, they can survive for a long time, even on the hands of cat owners. Once again, good old hand washing is the best defense.
So far, so good. All in all, toxoplasmata seem to be unpleasant but otherwise unimportant little critters if
you don’t happen to be pregnant. And, for many years, no one paid them much attention—but Joanne Webster’s fearless rats changed all that. In the 1990s, Joanne Webster was a researcher at Oxford University. She devised a simple but ingenious experiment. She placed four boxes in a small enclosure. In one corner of each of these boxes, she placed a small bowl containing a different liquid: rat urine, water, rabbit urine, and cat urine. Even rats that have never seen a cat in their lives avoid cat urine. They are biologically programmed to think, “If someone peed there who might want to eat you, don’t go there.” Furthermore, rodents have a general motto that goes something like this: “If someone places you in an enclosure with boxes containing urine, be on your guard.” Under normal circumstances, all rats behave the same way. They briefly explore the unfamiliar environment and then withdraw into one of the boxes with the less threatening urine in it.
But Webster found there were exceptions. There were rats that suddenly displayed completely atypical behavior. They inquisitively explored the whole enclosure, apparently oblivious to risk, even defying their instincts and entering the box containing the bowl of cat urine and hanging out there for a while. After observing them for longer, Webster was even able to conclude that they seemed to prefer the cat-urine box to the others. Nothing seemed to interest them more than cat pee.
A smell that should have registered in their brain as sign of mortal danger was suddenly perceived as attractive and interesting. These animals had become uninhibited seekers of their own downfall. Webster knew that there was only one difference between these rats and normal specimens—they were infected with toxoplasmata. This is an incredibly clever move on the part of the tiny parasites. They cause the rats offer themselves as food to their definitive hosts!
This experiment caused such consternation in the scientific community that it was repeated in other laboratories around the world. Scientists wanted to make sure the results were not a fluke so they tested to see whether their own lab rats would act in the same way if they were infected with toxoplasmata. And they did. The experiment is now considered flawless and scientifically sound. Scientists also discovered that the change in behavior was related only to the rats’ response to cat urine, while dog urine elicited the expected avoidance behavior.
These results whipped up a storm of debate. How could such tiny parasites influence the behavior of little mammals so drastically? To die or not to die? That is a huge question that any organism worth its salt should be able to answer—as long as there is no parasite on the decision-making committee. Surely?
It was not much of a leap from the little mammal to a larger mammal (that is to say, to human beings). Might it be possible to find human candidates who succumb to a kind of “feed myself to the cat” instinct in the form of inappropriate reflexes, reactions, and fearlessness? One approach to finding an answer to this question was to test the blood of people who had been involved in traffic accidents. The quest was to find out whether more of the unfortunate road users would turn out to be toxoplasma carriers than members of society who had not been involved in an accident.
The answer was yes. The risk of being involved in a traffic accident is higher among toxoplasma carriers, especially when the infection is in the active early stage rather than the later dormant stage. Three small initial studies were followed by a large-scale investigation, and all of them confirmed these results. The large-scale study involved taking blood samples from 3,890 Czech army recruits and testing them for toxoplasmata. The recruits were monitored in the following years and the number of accidents they were involved in was recorded and analyzed. Severe toxoplasma infection in conjunction with a particular blood group (rhesus negative) turned out to be the highest risk factor. Blood groups can indeed play an important role in parasite infections—some groups offer greater protection than others.
BUT HOW DOES our lady with the razor blade fit in to all this? Why is she not horrified by the sight of her own blood? Why is the feeling of slicing through her skin, flesh, and nerves processed not as painful but rather, as thrilling? How can pain have become the hot sauce in the otherwise bland soup of her everyday life?
There are various ways of approaching this question. One of them is to look at toxoplasmata. When we are infected with them, our immune system activates an enzyme (IDO) to protect us from these parasites. IDO breaks down a substance that the invaders like to eat, forcing them to enter the less active, dormant state. Unfortunately, this substance is also one of the ingredients needed to produce serotonin. (Remember: a lack of serotonin is associated with depression and anxiety disorders.)
If the brain lacks serotonin because IDO has snatched it all away from under the parasite’s nose, our mood can be affected negatively. In addition, nibbled-on precursors of serotonin can dock onto certain receptors in the brain and cause symptoms like lethargy. These are the same receptors as those targeted by painkillers—the result is indifference and sedation. It can take quite drastic measures to drag the brain out of that state of torpor so it can feel emotions keenly again.
Our body is a clever body. It carries out a risk–benefit analysis. When a parasite needs to be combated in the brain, the brain’s owner is likely to be in a bad mood. Activating IDO is usually a kind of compromise. The body occasionally uses this enzyme to snatch food away from its own cells. IDO is more highly activated during pregnancy, but only near the interface between mother and child. There, it snatches the food away from immune cells. That weakens them, making them react more mildly to the semi-alien presence of the baby.
Would the lethargy triggered by IDO be enough to drive someone to suicide? To put the question another way, what does it take to make people think about killing themselves? Where would a parasite need to start if it wanted to switch off our natural fear of harming ourselves?
Fear is associated with a part of the brain called the amygdala. Certain fibers run directly from the eyes to the amygdala, so the mere sight of a spider can trigger an immediate reaction of fear. This connection exists even in blind people whose visual cortex has been damaged by an injury to the back of the head. They no longer see the spider, but they still feel it emotionally. So, our amygdala plays a major role in the development of fear. If the amygdala gets damaged, a person can become fearless.
Examinations of intermediate toxoplasmata hosts show that the apartments the toxoplasmata occupy to hibernate in are mainly found in the muscles and the brain. Those in the brain are found in three locations. In descending order of frequency, these are the amygdala, the olfactory center, and the area of the brain directly behind the forehead. As we know, the amygdala is responsible for the perception of fear. The olfactory center could be responsible for the rat’s new-found love of cat urine. The third area is slightly more complex.
This part of the brain creates possibilities by the second. If a research subject is wired up to a brain scanner and confronted with questions about faith, personality, or morality, or if he is asked to complete complex and challenging cognitive tasks, lively activity is recorded in this region. One theory proposed by brain researchers is that this indicates that this area of the brain is drawing up many designs every second. “I could believe in the religion followed by my parents. I could start licking the desk in front of me during this conference. I could read a book and have a cup of tea. I could dress the dog up in a funny costume. I could film myself singing a jolly song. I could drive my car at breakneck speed. I could reach for that razor blade . . .” There are hundreds of possibilities every second, but which will win through and which will be carried out?
So, if you are a parasite with a plan, it makes sense to settle here. From here, it might be possible to promote self-destructive tendencies and weaken the mechanisms that suppress these courses of action.
Researchers wouldn’t be researchers if they hadn’t come up with the idea of repeating Joanne Webster’s experiment with human beings. So they had humans sniff different animals’ urine. Men and women who were toxoplasma carriers had
a different reaction to the smell of cat pee from those who were parasite-free. Men liked the smell considerably more, women less.
Smell is one of our most basic senses. Unlike taste, hearing, or vision, smells are not checked out before they make their way to our consciousness. Strangely, we can dream all sensory experiences except smells. Our dreams are always odorless. Truffle pigs know just as well as toxoplasmata that smells can trigger an emotional response. As it happens, the scent of a truffle is pretty similar to the scent of a sexy truffle pig male. When an infatuated female truffle pig smells a sexy male truffle pig hiding under the earth, she will dig and dig until . . . she discovers a disappointingly unsexy fungus for her owner. I think the astronomical price of truffles is more than justified when you consider how frustrating such a find must be for a poor sow. Anyway, the point is that smells can stimulate attraction.
Some shops exploit this phenomenon. Economists call it scent marketing. One American clothing manufacturer even uses sex pheromones to attract potential customers. In Frankfurt, where I live, you can often see long lines of teenagers outside the store’s darkened and pheromone-scented entrance. If the shopping precinct were closer to areas with free-ranging pigs, some pretty entertaining scenes might result.
SO, IF ANOTHER organism can make us perceive smells differently, couldn’t it also influence other sensory impressions?
There is a well-known illness whose main symptom is false sensory perceptions: schizophrenia. For example, people suffering from schizophrenia might feel like an army of ants is crawling all over their back, although there are no such insects anywhere nearby. They hear voices and obey their commands, and they can be extremely lethargic. About half to one percent of people suffer from schizophrenia.
There is much about the clinical picture of schizophrenia that is still unclear. Most drugs used to treat it do so by deactivating a signal transmitter in the brain that is overabundant in people with schizophrenia: dopamine. Toxoplasmata possess genes that influence the production of dopamine in the brain. Not all people who suffer from schizophrenia are parasite carriers—so that can be ruled out as the sole cause—but the proportion of carriers among those who suffer from schizophrenia is about twice that among those who do not.
Gut: The Inside Story of Our Body's Most Underrated Organ (Revised Edition) Page 17
