SARS-CoV2, a tiny string of RNA made of mere 30 thousand molecules (ribonucleotides) wrapped in a membrane stolen from the host, changed the behavior of us humans! Today, we walk around wearing masks, do frequent hand washings, soak in sanitizers, we feel nervous if someone next coughs or sneezes, and are socially distanced from other human beings. We refrained from celebrations & festivals, our old-time customs of shaking hands, hugs & kisses became ´risky´ practices. We closed schools, factories, offices, tourist venues for months, while turned our dwellings into offices/kindergartens and many parts of the world are under second round of lock down. As you know, all these strict measures are to protect the vulnerable, to avoid choking the health system and buy time until an efficient treatment protocol or vaccine appears for COVID-19. A few years ago, during an official visit to Japan, I felt a bit suffocating while watching several people wearing face masks in public transport. Now, I am walking around wearing face masks in buses and carrying hand sanitizers everywhere, quite surreal situation!
It is difficult to conceive that a microbe could alter the behavior of mighty human beings. SARS CoV2 is not a kind of virus that directly messes up our brain and alters our behavior. However, there are microbes that can mess up host brain and make them behave weirdly, such parasites can transform even humans! Those parasites perturb host´s nervous system, and propagate more efficiently by taking advantage of behavior manipulation. Let’s talk about some of such zombie pathogens.
Rabies virus – bullet shaped killer that make you aggressive
Rabies virus has a peculiar bullet shape (see the simplified diagram), and rabies infection is known to alter behavior of the host. Rabid ´´mad dogs´´ become more aggressive and less fearful, which increases the probability that the host will bite another animal, thereby spreading the virus to a new host before the rabid dog dies. The entire mechanism by which this deadly virus jumps from the bite site, the slow invasion & subsequent hijacking of host brain and the aggressive transformation of the host, still remains a mystery. The symptoms of rabies infection include anxiety, confusion, partial paralysis, agitation, hallucinations, and finally “hydrophobia´´. Hydrophobia is a behavioral alteration, the irrational ´fear of water´, caused by the difficulty in swallowing and painful muscle spasms. The infected person may panic at the sight of water, moreover, at a later stage even the thoughts of swallowing water may cause painful spasms. The patient will produce a lot of saliva and froth, which contains infectious rabies virus. Exact mechanisms of aggressive viral-manipulations of host brain are still unknown. Note, once the unfortunate host starts exhibiting clinical signs, it will be too late to rescue, however there are very effective vaccines against deadly Rabies virus.
Toxoplasma gondii- the kind, that can make you a risk-taker
Toxoplasma gondii´s intermediate host is cat. It is intriguing to know how these microscopic single-celled organisms reaches our cats, from an infected rodent. Toxoplasma infected rodents become extroverted and less fearful of cats, increasing its chance of predation and the parasite’s chance of completing its lifecycle. We can also get infected on consuming under-cooked infected meats or sometimes by cleaning an infected cat´s litter box. This parasite influences the behavior of humans, Toxoplasma infections can cause some mental illness and risky behavior like what happens with those infected ´fearless´ rodents. There were observations that women infected with the parasite exhibit slightly more suicidal tendency (though a causal link between infection and suicide attempt is lacking). This parasite can affect a specific area in brain called prefrontal cortex and interfere with the capacity of that brain region to apply ´brakes´. A scientific study describes a correlation between career risk-taking entrepreneurs and Toxoplasma gondii infection. Some researchers have linked Toxoplasma infection to human behavioral changes that position them at higher risk for car accidents and drug abuse. Again- this is just a correlation! Are we influenced by tiny microorganisms on our decision makings, we are only beginning to understand?
Hairworms- hijackers of insect´s mind
Hairworms or Gordian worms infect crickets/grasshoppers. These worms need water for mating while crickets prefer dry land. This parasite controls host´s mind to make a dive into water (which usually crickets hate!), and then escape from infected body. Hair worms hijack host brain by producing proteins to mess up cricket´s navigational system. Parasite-manipulated cricket jumps around and ends in water bodies, bingo! The worms come out, mate, lay eggs, which will be eaten by tiny insects in water, and those insects eventually end up in another cricket’s body. A complicated lifecycle, indeed! (see the attached video).
Cordyceps-the enslaver fungus
This zombie parasitic fungus, Cordyceps host on jungle ants. Once the fungal spore gets into an ant´s body, it creates chaos in host brain, makes the ant behave weirdly. The baffled zombie-ant, driven by the parasite wanders around to the top of a tree where it performs the final bite on a leaf and dies. Thus, finding a suitable environment, the fungus comes out of dead ant´s body, flourish and disperse more spores to enslave more hosts (see the attached video).
The above-mentioned cases are some classic examples of how the microbial/parasitic infections can affect the behavior of mighty hosts. Mechanisms underlying such behavior alteration by microorganisms are mostly poorly understood, will be very interesting research area indeed. Our genome is the ´graveyard´ of prior viral infections, which might have happened to our earlier ancestors. A significant portion (8.3%) of human genome is made of remnants of viral genomes. Several of those viral elements get repurposed or ‘exapted´ for several cellular functions including neuronal functions. We believe, we are in good control of our behavior, but who knows, how much we are influenced by tiny microbes or their exapted genes? We are only beginning to understand how such infections impact our behavior.
During this pandemic time, SARS CoV-2 modified us but taught us several lessons as well; it revealed us how poor we are in terms of pandemic preparations, reminded that we are as vulnerable as any other fellow creatures that shares this planet, it showed the values of social and family life, how vital the basic research is, the relevance of sharing knowledge & technologies and the significance of simple hygiene practices. We witnessed the rejuvenation of nature during lockdown, appealing us to stall our merciless destruction of nature. Though indirectly, this ´bat virus´ forced us to alter human behavior. How these pandemic-influenced behavioral changes will affect our future; whether such ´changes´ may remain permanent and transform into the new ´normal´ in our lives?… is an empirical question!
References
Rabies virus
https://www.nature.com/articles/s41598-017-12726-4
https://www.medicalnewstoday.com/articles/319735
Parasitic manipulation
https://www.sciencedirect.com/science/article/abs/pii/S0376635704002049?via%3Dihub
Hairworms
https://www.newscientist.com/article/dn7927-parasites-brainwash-grasshoppers-into-death-dive/
https://royalsocietypublishing.org/doi/10.1098/rspb.2005.3213
Toxoplasma gondii
https://www.discovermagazine.com/mind/how-a-worldwide-parasitic-infection-might-shape-human-behavior
Domestication of retroviral gene-Syncytin and Placenta
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3000028
Neuroscience and molecular tools 
It was a good informative read. 👍👍
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Thanks 🙂
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Well written Raji chittappa. Hope you are doing well chittappa.
P.S.: Reading this post reminded me about another parasite known as Leucochloridium found in snails I think. The videos about it are really worth the watch.
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Dear Sanjay, yes we are doing great, hope you are also :).
Indeed, Leucochloridium is also a mind-controlling parasite. There may be even more, just picked some. Saw the videos of Leucochloridium, agree with you, worth watching !
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