Early studies of toxoplasmosis have found that they can have a significant impact on the brains and behavior of mice, making them less anxious and more curious. Cats are more susceptible to totosis when they are more likely to be caught by cats. As one of the most prolific parasites on Earth, toxoplasmosis can infect almost any warm-blooded animal. In addition, some scientists believe that it may have infected more than 3 billion people, but it has largely shown no harm.
Toxoplasmosis life cycle (pictured from: CDC, via Cnet)
Toxoplasmosis and malaria parasites belong to the same class of “outstanding” single-celled organisms, known for their ability to change the behavior of rodents and humans. The public and researchers have long been curious about how it works.
Studies have shown that rodents infected with toxoplasmosis become more “fearless”, and some researchers have even linked human infections to mental health conditions such as impulsive/schizophrenic disorders.
In most warm-blooded mammals, toxoplasmosis is essentially an inert presence and is called a protective cyst to survive (including in brain tissue). The cyst will remain in the host body for life unless the TA’s immune system weakens.
In the cat’s gut, however, things are very different. Toxoplasmosis has only one goal – to enter the cat’s body, mature, successfully reproduce, and to drain the offspring from the host with the feces, and then start a new cycle.
To increase the cat’s ability to infect, toxoplasmosis will first look for rodents to “bravely” face the cat, rather than being scared away by its smell.
In this respect, toxoplasmosis seems to reduce anxiety and increase the chance of it being eaten, giving it the opportunity to sneak into a “better quality” host.
For cats, furry rodents are more like a Trojan horse, carrying a group of parasites that are sneaking into their bodies.
Toxoplatic cysts buried in brain tissue (pictured: CDC)
However, there is still a heated scientific debate about the degree of toxoids’ ability to “change their minds”. Studies have shown that the creature does affect the behavior of mice, but is it an evolutionaryly stimulating adaptation mechanism? Will it directly manipulate the host’s brain and do everything as it wants?
Or does the infection cause the host’s immune response to become disordered, leading to encephalitis, and a change in behavior? A new study, published Tuesday in the journal Cell Reports, tries to answer these questions.
The researchers examined changes in the behavior of mice infected with toxoplasmosis and conducted a series of behavioral tests on rodents to determine whether they became unafraid of predators’ odors and open spaces.
Then drill into the brains of mice and focus on the genetic markers of parasitic cysts and inflammation to determine if there have been significant physiological changes that can help change the behavior of mice.
“There is still a lot of debate about whether general anxiety is reduced,” said study co-author Madlaina Boillat, a neurogeneticist and doctoral student at the University of Geneva.
Studies have shown that infected mice have no changes in anxiety (increase disonire), depending on more variables. For example, which behavioral criteria are used, and the level of infection, remains largely dependent on the strains of laboratory mice and parasites.
In one behavioral test, the researchers placed the mice in an X-shaped “maze” with both ends surrounded by large walls and the other ends open.
For safety reasons, uninfected mice are mostly glued to arms with boundary walls. But mice infected with toxoplasmosis will spend more time exploring the open space.
Another test showed that infected people were also more likely to smell foxes and guinea pigs. This new finding is particularly important because it proves that toxoplasmosis does not have the anecdotal “fatal attraction” shown. That is, selectivemanipulation of the host’s behavior to reduce fear of cats.
Instead of sending cats to death, rodents appear to be linked to a wider range of anxiety pathways in the brain, triggering a surge in curiosity.
RNA sequencing experiments have shown significant changes in the brains of infected mice, Boillat said. Highly infected people show signs of immune pathology, such as neuronal death and excitatory toxicity.
The severity of these symptoms was associated with spherical cysts and the degree of validation found in the brains of mice. Toxoplasmosis does not directly mess up brain cells (such as brain gray matter in some way to mobilize rodents) for their own benefit, but rather promotes inflammation.
There have been studies that have shown similar phenomena: when cysts and inflammation worsen, the activity levels of infected mice change accordingly.
In other words, toxoplasmosis does not have the ability to ‘control the mind’ on the host, but rather is more like an immune response that drives abnormal, even deadly, behavior.
If the findings can be found in the human body, it could have far-reaching consequences. Boillat points out that it is well known that either archie filling or inflammation of the brain caused by other pathogens can trigger mental illness in humans.
However, in interpreting the results, great caution should be exercised. The team observed a strong correlation between gene expression and behavior in the infected brain, but could not provide any explanation of causation.
In addition, humans and mice respond differently to parasitic infections, making it difficult to conduct direct cross-species comparisons.
Next, the team will look at how inflammation in the brain drives changes in mouse behavior.
Is it because brain cells are subjected to some degree of transition already stimulation, or is it because molecular signals are beginning to confuse? Does the presence of parasites alter the way the brain responds to stimuli?
To answer these questions, further clarification is needed on toxoplasmosis’s so-called ‘mental control’ technique. For the ‘shovel officers’, follow-up studies can also help reduce their fear of the stars.