The Toxoplasma Gondii (T Gondii) parasite really is the stuff of horror movies. The parasite, once in the brain of rats and mice, mutes their fear of cat urine, bringing them to their furriest predator on a figurative plate. The parasite, in other words, gets to its desired destination by using the host as a kind of suicidal Uber.
But the pesky parasite doesn’t stop there. It can – and does – infect humans, usually via cat litter or uncooked meat. As many as two billion people are said to be infected with the parasite, although it’s unlikely that is what T Gondii intends, given we’re (for now) at the top of the food chain. That doesn’t mean the parasite doesn’t impact us, though. Evidence suggests it’s linked to all kinds of subtle changes affecting risk and extroversion, and has even been linked to an increased chance of suicide or developing schizophrenia.
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And it could be worse than we feared, according to new research from 16 institutions, which argue the parasite might alter – and sometimes amplify – a number of brain disorders including epilepsy, Alzheimer’s, Parkinson’s as well as some forms of cancer.
The researchers came about their findings by analysing data from the Congenital Toxoplasmosis Study, which has been monitoring 246 infants with congenital toxoplasmosis (the infection T Gondii triggers). Fragments of microRNA and proteins found in those severely affected matched up with biomarkers associated with patients suffering from a range of neurodegenerative conditions such as Parkinson’s and Alzheimer’s. The epilepsy link, on the other hand, is down to the way the parasite disrupts communication between GABAergic neurons. The cancer connection is possibly the most disturbing, as the researchers found a link between T Gondii and nearly 1,200 human genes linked to various types of cancer.
“We suspect it involves multiple factors,” explains the University of Chicago’s Rima McLeod. “At the core is alignment of characteristics of the parasite itself, the genes it expresses in the infected brain, susceptibility genes that could limit the host’s ability to prevent infection, and genes that control susceptibility to other diseases present in the human host.”
It’s not that the researchers are arguing that T Gondii causes Alzheimer’s, Parkinson’s, epilepsy or cancer – just that a side effect of the parasite’s habit of meddling with brain proteins is possibly making people more susceptible to them. That, though, is worrying enough and changes how we approach all of them.
“This study is a paradigm shifter,” said the paper’s co-author Dennis Steindler, director of the neuroscience and aging Lab at Tufts University. “We now have to insert infectious disease into the equation of neurodegenerative diseases, epilepsy and neural cancers.
“At the same time we have to translate aspects of this study into preventive treatments that include everything from drugs to diet to lifestyle, in order to delay disease onset and progression.”
Some estimates reckon that half the world’s population will be infected with T Gondii eventually, so more research into the parasite’s side effects is certainly welcome. A severely infected cat can excrete as many as 500 million parasite-carrying oocysts, and just one of those is infectious – even if it’s been left in soil or water for a year. Nature is horrible, isn’t it?
Images: D Ferguson, Oxford University and Tambako the Jaguar
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