Imagine a cat readying itself to pounce on a mouse. The mouse notes the feline but does not budge. Soon, it is cat food. The parasite Toxoplasma gondii was looking for a definitive host. Lodged inside the rodent’s brain, the microbe manipulated the mouse to release dopamine, a mood regulator that causes extreme emotions:
euphoria, depression. Its central nervous system doped on dopamine, the mouse’s survival instincts were lulled. Thereafter, life seemed pleasant, the cat friendly. T gondii survived.

Now imagine further. The cat’s owner is a pregnant woman. It is possible that her unborn child would become a schizophrenic. The pregnant woman takes out the cat litter, wanders into the kitchen and bites into an apple—without washing her hands. The parasites reach her brain via the bloodstream. The dopamine spell follows, changing the woman’s personality. It makes her feel guilty and duty-conscious. The microbe then makes its way to the foetus through the placenta, leaving it vulnerable to a mental disorder someday.

Most schizophrenics are known to have high levels of antibodies against T gondii in their blood. At the same time, some studies noted that individuals infected by T gondii were bound to exhibit symptoms of schizophrenia.  E F Torrey studies schizophrenia at the Stanley Medical Research Institute in Bethesda, USA.  He and his team treated infected and oddly behaving rats with anti-psychotic drugs used to suppress schizophrenia. The drugs blocked the tachyzoite formation (a stage where the microbe divides and increases its number). As the microbes died, dopamine levels went down and the rats were not as foolhardy.

Life began with microbes

Life on earth began with microbes. To colonise humans, the microbes made lifestyle changes. They had to match the host’s way of life, which was not going to be easy. Early humans were nomadic. To understand human-microbe relationship at this stage, scientists studied a handful of tribes left in the world. People in these tribes wander in small, isolated groups; their contact with people from other groups is rare.
If the microbes wanted to survive off such people, they, too, would have had to follow suit, inferred anthropologists. Since the microbes were isolated along with the people, it made no sense to overcome the host’s immune system, turn virulent and kill the host that provided it with very few chances of moving on to another one.
A 2007 DNA study at the University of Utah, USA, confirmed the pace of human evolution increased after agriculture became widespread. It was time the microbes changed their lifestyle; they became more infectious. The Human Immuno Deficiency Virus (HIV) is believed to have made the jump from wild monkeys to humans.

Why microbes succeed

A peek into the life of the bacterium Helicobacter pylori indicates why microbes have succeeded. H pylori is common to the human stomach. The medical establishment decided to eradicate it from the human gut. H pylori is disappearing, but the bacterium has beneficial effects on the human body, said microbiologist Martin Blaser in 1996. It produces alkaline chemicals to neutralise stomach acids, protecting against acid reflux, explained Blaser. The question is: why would the microbe help the host? The chemicals the microbe produces help the host survive and prevent other pathogens from lodging in the digestive system.

Nature has billions of microbes and thousands inhabit the human gut. The host immune system restricts gut microbes within the gut. More often than not, the rebels within the system are squashed. Over the years, natural selection has favoured the evolution of helpful microbes. The human body wears an external suit of millions of microbes. Some skin areas maintain a microbial population that does not vary over time, like the ears, the nostrils and creases on either side of the nose. In between the toes alone, there could be 10 million microbes in a square centimetre.

Under the microscope

Using genetic analysis, researchers are creating an inventory of microbes that come with humans. They are gathering information under the Human Microbiome Project, an offshoot of the Human Genome Project that mapped the human DNA.

When the genome map was created, scientists found we have 20,000 functioning genes, putting us in the same category as worms. Then they realised they had forgotten the microbes. The new exercise can be defined as a ‘them-plus-us genome project’, one that says humans cannot understand themselves if they do not know microorganisms that make them who they are.

With science learning about microbes everyday, the idea of human agency will undergo corrections. It will change the way we look at microbes.

Down To Earth Feature Service