Half of the world’s population is infected by the ‘cat parasite’ Toxoplasma gondii, and in certain areas, the infection rate is an astonishing 95%. Unless you go for a series of tests, there is absolutely no way of knowing whether you’re infected or not. This parasite has been associated with a number of mental disorders, such as bipolar disorder and schizophrenia. It has also been blamed for an increase in severe depression and subsequent suicide.
Yup, that’s right, Toxoplasma is everywhere, and while the jury is still out on how detrimental this parasite is to our health, scientists have finally found out why it’s so good at dodging our immune’s system.
For the uninitiated, Toxoplasma is a cat-borne parasite that causes Toxoplasmosis – a disease which is asymptomatic in healthy people, but can lead to a whole range of other disorders in those with compromised immune systems, such as the elderly and pregnant women.
The Czech evolutionary biologist, Jaroslav Flegr, is the man at the forefront of this research into Toxoplasma. He once stated that this parasite “might even kill as many people as malaria, or at least a million people a year,” due to its apparent ability to change our responses to harmful situations.
Past research has concluded that when mice are infected by this parasite, they lose their instinctive fear of cat urine, and display signs of an impaired memory. It has been hypothesized that Toxoplasma messes with a rodent’s brain so that it can complete its lifecycle (see below), and for many years now, scientists have been investigating if something similar occurs in humans.
Parasite researcher, Chris Tonkin, from the Walter and Eliza Hall Institute in Australia, declares that “there is a fascinating association between Toxoplasma infection and psychiatric diseases including schizophrenia and bipolar disorder.” While there definitely appears to be something weird going on with people infected by this parasite, the scientific evidence, so far, is frustratingly inconclusive. However, there is one thing we certainly do know about Toxoplasma and that is that it has the ability to manipulate our immune systems.
The fact that in specific areas of the world, almost the whole local population is infected goes to show just how successful this parasite is – and its success lies in its ability to strike an incredible balance with our body’s immune system. This parasite has impressively managed to keep our body’s immune response to it low enough that it can survive inside us, but high enough so that those who are infected can live a healthy life acting as one big parasite incubator.
And finally, scientists have figured out how it does it.
Matthew Bowler, from the European Molecular Biology Laboratory, declares that “the parasite rewires the host’s inflammatory response – it completely subverts the chain reaction that would normally trigger our body’s defenses.”
In normal situations, when your cells detect the presence of a parasite, a number of molecular signals will activate the protein p38a, prompting it to move into the cells’ nuclei. Once here, it triggers the genes that activate an inflammatory response to destroy the pathogen. Interestingly, rather than just simply blocking these signals, this parasite does the complete opposite. Bowler, and his team of researchers, found that Toxoplasma actually kick starts the human inflammatory response, and then manipulates it according to its own needs.
This research by Bowler was based on a previous study by Mohamed-Ali Hakimi from the Institute of Advanced Bioscience in France, who found out that Toxoplasma secretes a protein known as GRA24 that triggers the protein p338a directly, before the body’s immune system has a chance to do so itself.
The team has now found out that GRA24 binds more strongly to p33a than the cell’s own proteins do, which allows the parasite to control the level of immune response that is dished up by the body. At the same time, this GRA24 protein prevents the body from turning off the inflammatory response, which is why this parasite is so dangerous in those who have weakened immune systems. The team concludes that “the tight control of the inflammatory signaling prevents either too weak a response leading to host death, or too strong a response preventing invasion.”
While it is a bit concerning that this parasite can manipulate our whole immune system, this research could help scientists to develop more effective anti-inflammatory drugs.