Can a parasite control your mind?
A single-cell parasite, Toxoplasma gondii, is perhaps best-known for its connection to cats. The parasite can move from its feline host to humans, most commonly through contact with cat feces. And while the parasite typically only causes mild infection (people may have flulike symptoms), in people with weakened immune systems, infections can cause serious problems, from seizures to severe lung problems.
But a T. gondii infection can also have some downright bizarre effects. Over the years, the parasite has not only surprised and stumped researchers, but has also led to new insights into how human behaviors work.
T. gondii has been shown to increase fearlessness in rats.
Rats infected with the parasite seem to lose their typical fear of cats, and more specifically, their fear of cat urine. A 2011 study in PLOS ONE suggested that infected rats start to feel a type of “sexual attraction” to the smell of cat urine, rather than their usual defensive response to the scent.
This might be because a T. gondii infection changes neural activity in certain areas of the brain, the researchers said. The parasite “overwhelms the innate fear response” so that rats no longer avoid the scent of cat urine, they wrote. Instead, the amorous rats are drawn to it — and to their deaths.
T. gondii can leap between almost all warm-blooded animals.
Cats and rats aren’t the only animals that can host the parasite. T. gondii is an exceptional parasite in that it can leap from almost any warm-blooded creature to another. Although an estimated 6 in of 10 infectious human diseases are zoonotic (meaning they can hop from animals to humans), hardly any share T. gondii’s wide versatility of host organisms, according to the Centers for Disease Control and Prevention.
Scientists haven’t pinpointed exactly why this is, but some research, such as a 2011 study published in the Proceedings of the National Academy of Sciences, suggests that at least part of the answer may be found in the parasite’s proteins: When a certain type of protein is removed, the parasite is no longer virulent. Researchers speculate that this is because those proteins disrupt key proteins in the host’s cell that are key to the host’s immune response. [10 Deadly Diseases That Hopped Across Species]
Others suggest that T. gondii could contribute to other types of mental illness, even suicide.
Schizophrenia isn’t the only psychological disorder that is possibly linked to T. gondii. A 2011 study that was done in mice and published in the journal PLOS ONE showed that the parasitemay cause infected brain cells to release high levels of the neurotransmitter dopamine.
Increases in dopamine could play a hand in certain mood disorders, such as bipolar disease, which has been linked to dopamine irregularities, according to the study. Other research done in humans suggests that Toxoplasma could be connected to impulsivity, and even suicide.
The parasite wouldn’t be the first pathogen to alter people’s brain and behavior: The rabies virus, which is deadly in people, has long been shown to have devastating neurological effects.
The Sci-Fi 