If you believe we’re the master of our actions, think again. Better yet, have a fungus, bacterium, or protozoan tell you what to think. Jedi mind tricks are nothing compared to what microbes can do to animals, human and otherwise.
You’ve likely heard that mice and rats infected with Toxoplasma gondii, a protozoan parasite that causes toxoplasmosis, lose their fear of cats because the pathogen initiates “epigenic remodeling.” In other words, T. gondii changes the expression of rat DNA to its advantage. As a result of this “remodeling,” infected rats and mice become sexually aroused by cat urine and seek it out, to their detriment obviously. In this way, T. gondii infects more cats.
A recent finding is that when kids get a T. gondii infection, they’re at a higher risk of mental-health crises as adolescents. Research published in August 2014 in the Journal of Nervous and Mental Disease found a strong correlation between T. gondii infections and diagnoses of schizophrenia, depression, aggressive behavior, and impaired cognition in young adults. However, the authors stopped short of claiming this is a direct result of toxoplasmosis.
Now let’s talk about gut feelings. As you may be aware, most cells in our bodies are not human. About 57% belong to microbes, and the rest are “us.” Beyond a doubt, our gut bacteria strongly influence our emotions and behavior. Bad bowel bugs can also make us ill, but not in the “cruise ship crud” sense. Recent studies point to a common source of some cases of obesity, Parkinson’s disease, and clinical depression: faulty feces.
In the US, Canada, and many other countries, “fecal material transplants” or FMTs are becoming more widely recognized as a treatment option for certain maladies. FMTs have proved especially good at reducing symptoms of depression; improvements in many cases are nothing short of stellar.
Simply put, poop from healthy donors having robust and diverse gut-microbial communities is transferred to sick patients with depleted gut-microbe populations. I read that fecal donors are more carefully screened than sperm donors are. I imagine they have less fun donating, too.
Let’s look at the fungus among us that turns insects into zombies. In 2018, Cornell University biologists found that a native fungus, Batkoa major, had killed off a large number of spotted lanternflies (which are not actually flies, but whatever). This was a happy massacre, as lanternflies are invasive and harm vineyards, orchards, and forests.
It seems that when Batkoa spores contact a lanternfly, they enter the bug through leg joints and other chinks in its armor. Once inside the bug’s exoskeleton, Batkoa starts to multiply. Soon it overwhelms the insect, which stops eating, mating, or anything else fun. Somehow, the fungus then directs the lanternfly to climb someplace high, like to the end of a tall plant.
As its ghoulish choreography unfolds, Batkoa prompts the lanternfly to open its wings to expose its abdomen. That is the bug’s final move. The fungus then exudes threadlike hyphae from the corpse, “sewing” it to its perch. A day or so after the lanternfly’s death, Batkoa spores explode from its belly, showering all below with powdered death.
Death by fungus is as old as the dinosaurs. In 2021, Oregon State University scientists found a 50-million-year-old ant preserved in amber. The poor thing had a parasitic mushroom sprouting from its anus like an umbrella. Toxoplasmosis sounds like a picnic compared to a brain-hijacking fungus that controls your final acts, kills you, and launches a spore-laden parasol from your butt.
But these things barely register on the creep-o-meter. Entomophthora muscae, though, maxes it out. This fungal pathogen, used commercially to kill flies in limited settings, delights in turning a range of well-adjusted flies into ardent necrophiliacs. Its host list comprises over twenty species in eight families, including some which spread human diseases. While it is native and endemic, it was not until 2022 that details on its deviant ways were exposed.
In a joint Swedish-Danish study published on July 13th, 2022 in the ISME Multidisciplinary Journal of Microbial Ecology, authors Naundrup, Bohman et al reveal how this fungus uses necrophilia to create untold bonus victims without lifting a finger. Or a hypha. If you don’t think “simple” life forms are intelligent, this might give you pause.
As with our hapless lanternfly, forced by Batkoa to aid in its own murder, flies have their free will hacked as E. muscae takes over their bodies. Although it kills both fly sexes, females get the usual consumption from within, a forced march to a prominent spot of the pathogen’s choosing, swiftly followed by death.
Male flies, on the other hand, are compelled to have sex until they die. In spite of the fact more than a few guys reading this probably think, hey – that might not be such a bad ending, rest assured it’s no fun for guy-flies.
Once a female victim is good and dead, E. muscae begins making sesquiterpene analogs to the female fly’s alluring sex pheromone. Countless males line up to copulate with her corpse, in the process getting fatally infected by spores. One curious tidbit from the study is that the longer a fungus-killed female rots, the hornier the males get. E. muscae saves itself a pile of work, as one cadaver infects dozens more flies.
Illustration: Lifecycle of Toxoplasma gondii courtesy CDC.