A brain parasite believed to infect nearly a third of the UK population has been found to evade immune detection by hiding inside brain cells and releasing signal molecules that silence alarms to the immune system. The protozoan parasite Toxoplasma gondii is believed to have infected about half of the global population, according to some estimates. In most people the parasite is dormant and causes no visible symptoms. The dormant parasite in some people can be activated, causing neurological damage and birth defects in children. People who are pregnant or have compromised immune systems should take measures to avoid contracting the parasite.
The research was conducted by the Walter and Eliza Hall Institute, who used advanced genomics technology to track the parasites in real time.
Ushma Ruparel, a PhD student on the team said: “We know that Toxoplasma parasites make their own molecules and proteins that it exports into the host cell to protect itself from detection by the immune system.
“While this is well-understood in the acute, initial stage of infection, how Toxoplasma hijacks its host cells in its dormant form is unknown.
“With our colleagues who have expertise in genomics and advanced imaging, we showed that the parasite exports proteins called Inhibitor of STAT1 transcription (IST) to the host cell to suppress immune signals.”
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The IST protein prevents the cell from producing signalling molecules called interferons.
Associate Professor Christ Tonkin said: “Interferon is crucial in the fight against disease.
“However, the cunning parasite tries to turn this signal off during the latent period, as this is the only way it can survive.
“While the immune system is determined to rid the infection from the body, the parasite only has survival on its mind. So, it’s essentially a tug-of-war, a molecular battle.”
Associate Professor Tonkin speculates that this research could provide advances in understanding for a large number of chronic diseases.
“Diseases such as HIV, hepatitis, malaria and tuberculosis are all examples of chronic or latent infections that cause significant disease, disability and economic impact.
“If we can understand what causes these latent infections to reactivate and their control over our cells and brain, we will be on the pathway to finding new treatments that diminish this burden for some of the most underprivileged people around the world.”
Similar to toxoplasmosis, tuberculosis has a startlingly high prevalence of 24.8 percent, with most cases latent and asymptomatic.
Toxoplasmosis can be found in cats, and it can spread when cleaning their litter tray.
The NHS notes that you cannot catch it directly from stroking cats or from contact with another human who has the parasite.
A common vector is meat products, with the NHS recommending that people at risk avoid unpasteurised milk and taking care when handling raw meat.
A strong association has been seen with beef in particular.
Toxoplasma gondii has been correlated by some studies to increased rates of schizophrenia, bipolar disorder and Alzheimer’s disease, but a causal relationship has not been determined.
The intended hosts for the parasite are cats and the small mammals they prey upon like mice.
Toxoplasma infection in rodents has been shown to alter brain chemistry and remove their innate fear of cats.
This change benefits the parasite as when the cat eats the rodent, the cat becomes infected.
Researchers note that the risk of a cat eating a human being is “infinitesimally small” but not zero.
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