“Sometimes we think we decide… and a microorganism decides”

An invisible world of microorganisms, often associated solely with disease, possesses the remarkable ability to manipulate the behavior of living beings to enhance their own survival. Jesús del Pozo, a professor of Microbiology, explores this phenomenon in his book "Microorganismos, cerebro y control mental" (Microorganisms, Brain, and Mind Control), presenting real-life examples that blur the lines between science and fiction.

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We carry millions of years of coexistence with viruses, bacteria, fungi, and parasites. Some have even learned to manipulate us.

These microscopic entities can transform insects into "zombies," enable parasites to suppress fear in their hosts, and even influence human sleep, aggression, and mood. Del Pozo explains that when infections reach the human brain, they can alter personality, conduct, and emotions. He highlights the "sleeping sickness," where the parasite inverts the host's sleep cycle to match the activity of the tsetse fly, the disease's vector.

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The parasite inverts the sleep cycle: we sleep during the day and stay awake at night. Why? Because the tsetse fly is diurnal. If we sleep during the day, we are an easier prey. It's a three-way strategy.

Del Pozo further elaborates on how infections can impact emotions, citing Lyme disease as potentially fostering more aggressive behaviors. Rabies serves as a stark example, with the virus traveling to the brain, inducing extreme aggression and violence that facilitates its transmission through saliva. He notes that myths of werewolves may have originated from historical rabies outbreaks.

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Yes, rabies is a very clear example. The virus travels through the nervous system to the brain, causes extreme aggression and violence, and that favors its transmission through saliva.

While microorganisms may not possess conscious decision-making capabilities, del Pozo confirms they can influence instincts related to sleep, feeding, aggression, and sexual behavior. They achieve this by modifying neurotransmitters and other substances that regulate human conduct. The gut microbiota also plays a role, influencing our feelings by promoting the production of substances like serotonin and dopamine.

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Saying yes would be attributing to them the capacity to think and develop strategies, and we don't know that. What we do know is that, through different mechanisms, they can influence our behavior.