Humans have been battling parasites since the beginning of mankind. They have taken the form of worms, microbes, bacteria and viruses; having the simple aim to take over our bodies and use them for their own benefit. No matter how we try to fight them off, it is only a temporary win as these parasites change and adapt in order to get ahead once again.
Parasites have the uncanny ability to alter the ways in which human bodies function, they can even alter cognitive capacity in some cases! Modern medicine and science tell us more about these parasites as we begin to understand their inner workings. As much as they are considered a nuisance, it sometimes helps to know exactly what you could be up against.
In this book summary readers will discover:
- The battle between humans and parasites
- How parasites use others to their advantage
- Parasites can create zombies
- Bacterial emotions
- How parasites have changed cultures around the world
Key lesson one: The battle between humans and parasites
The battle between humans and parasites has gone on for thousands of years somewhat unnoticed. This is partly due to the fact that it is fought mostly on a microscopic level. The reality is that this battle has been around for so long, that our very bodies evolved along with it. Just consider the defences that the human body has developed – Hairs in our noses to filter out potential parasites, our multi-layered skin – even our eyes produce tears to get rid of any foreign bodies. This is just on the outside of the body. Internally, there is an entire system of defence mechanisms in place. Mucous, stomach acid and our immune system all work to get rid of anything that is not supposed to be present in the body.
Just how humans have developed defences, parasites have good offensive strategies as well. Firstly, they have the numbers. There are definitely more of them than there are of us. Secondly, they can reproduce at an astounding rate, thus making eradication problematic and lastly, they are highly adaptable. These three traits make parasites a formidable enemy. Even if we manage to kill most of them, a few survivors can mutate and rapidly multiply getting us right back to the start of the battle. It’s what we go through every year during flu season. It is also what caused some of the memorable parasite-related deaths in history – the bubonic plague, smallpox, measles and the Spanish Flu. These events killed more people than actual wars that have been fought.
And the battle continues. With each defence mechanism we develop, parasites resist, adapt and evolve to come back stronger.
Key lesson two: How parasites use others to their advantage
Parasites don’t infect us with the sole intention to kill us. No, they want to use others as a resource for their benefit. In doing so, they can change cause a change in behaviour in infected individuals. Yes, it does sound like a plot to a horror movie, but it is actually a common occurrence. Tapeworms, for example, enter brine shrimp and then push them to mate in order for the tapeworm to pass themselves on to a new host. When tapeworms infect shrimp, the colour of the shrimp’s shell turns pink which cause them to be easily spotted in the water by the flamingos that usually feed on them. The flamingos eat the shrimp and become the next host for the tapeworm. The tapeworm reproduces in the flamingo and its eggs are released in the flamingo’s excrement which goes back into the water. This is the complete life cycle of the tapeworm in which it influences the behaviour of the shrimp and flamingo in order to reproduce. The shrimp are held hostage and made to mate and the colour change makes the shrimp easy pickings for the flamingo who remains in this habitat because the food is easy to spot as compared to transparent shrimp elsewhere.
This is how intelligent parasites are and it happens not only to animals, but humans as well. Guinea worms are parasitic worms and their larvae are carried by fleas. These fleas are ingested by humans via drinking water. Stomach acid kills the fleas immediately but the larvae survive, mature and reproduce within abdominal muscles. When the female is ready to release her eggs, she moves to the connective tissue of the legs. The worm moves to the surface of the skin and releases an acid that causes the skin to blister. The natural instinct of humans is to rinse their legs to get rid of the burning sensation that accompanies the blister. The worm breaks through the skin and releases its eggs into the water during this time. The parasite uses our own natural instinct against us.
Key lesson three: Parasites can create zombies
Well, if the worms were not enough of a horror movie for you, there also exists some parasites that can create zombies.
The jewel wasp is a prime example. Thankfully, its target is usually cockroaches. It injects a poison into a roach’s brain that has an effect on a neurotransmitter that controls movement. All the wasp has to do is hold onto the cockroach’s antennae to control it – effectively making it remote-controlled. The wasp leads the cockroach into a burrow and lays its eggs on it. Whilst waiting for the eggs to hatch, the wasp can even inject the cockroach again to make it groom itself and remove any other parasites from its shell thus keeping the wasp eggs safe. When they hatch, they will feed on the cockroach which is still alive but unable to move.
Are you creeped out yet? If not, parasites can manipulate the brains of humans as well. The roundworm, Toxocara, enters the human body after coming into contact with infected animal faeces. The worm remains in the larval stage inside the body and moves around to the different organs. In 2012, a study showed that when infected with this parasite, kids between the ages of 6 and 16 have significantly worse comprehension and math skills.
Key lesson four: Bacterial emotions
Humans have parasites living in their bodies from the day they are born. How? Well, the microbes and bacteria present in our gut are technically parasites. They actually play a much bigger role than just helping within which digestion. These organisms release dopamine, GABA and serotonin are chemical neurotransmitters that have an effect on our emotions. This is why a happy gut is so important to maintaining a happy and energetic mood.
There have been experiments conducted to prove that p was these microorganisms affect our emotions. In 2013, three groups of women were monitored for a month. The first group was given probiotic yoghurt twice daily, the second milk, and, the third, was a control group that received neither. At the end of the month, the women were subjected to MRI scans whilst being shown images of faces displaying different emotions. The women in the first group were shown to be less disturbed by the images depicting negative emotions that the others. The bacteria that they consumed for a month had a positive impact on their brains.
Key lesson five: How parasites have changed cultures around the world
The ways in which parasites affect cultures around the world are subtle and would go on undetected if we did not highlight it. It is still debatable if this is really the case, however,
instead of directly adapting our cultures to avoid parasites, we have actually done it to avoid infection.
To give you examples of this, biologists have found that those cultures that prefer to live in groups are found predominantly clustered along the equator. This is an area with high parasitic infections. They also found that these people prefer spicier food which is known to kill bacteria and prevent infection. Psychologists have also found regions with high parasitic infection are home to less outgoing cultures. It is theorised that this introverted lifestyle could be a result of avoiding infection by staying away from others.
These cultural preferences can also be extended to things like washing hands before prayers, bowing instead of shaking hands as a greeting and even strict commitments to partners. If you think about it, these all minimize the risk of infection by parasites.
The effect that parasites have on culture may have been what initiated the behaviour a long time ago and they still exist today on some level. It is the same as how parasites have developed their own culture to ensure their survival through the ages.
The key takeaway from This is Your Brain on Parasites is:
Parasites have been around for thousands of years. Humans have developed many defences against parasites but parasites keep adapting to ensure their survival. The way in which a parasite can affect its host can vary but in all cases, they use their host as a resource that will help them fulfil their goal of reproduction. Parasites can manipulate their host’s behaviour, actions, processes and even appearances in some cases. It is pretty impressive for organisms that are, for the most part, tiny little organisms that cannot survive on their own.
How can I implement the lessons learned in This is Your Brain on Parasites:
Ensure that you follow good hygiene practices at all times! Actually, the lessons learned in this book summary is not something to be implemented but rather to be considered. Parasites and humans both have found ways to battle each other throughout the ages. When one pushes back, the other comes back fighting harder and with a different tactic. This will probably not end any time soon.
