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Parasite that ‘hijacks’ host cells could alter brain behavior

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Scientists from Melbourne's Walter and Eliza Hall Institute have discovered how a common parasite hijacks host cells where it lies dormant for a long time. In doing this, it also possibly alters the host's behavior or personality.

Toxoplasma is a common parasite that is transmitted by cats and also found to exist in raw meat, and around 30% of the population is infected with this parasite. Dr. Chris Tonkin, Dr. Justin Boddey, Dr Alex Uboldi, Mr. James McCoy and Mr. Michael Coffrey of the Walter and Eliza Hall Institute spearheaded the study.

Dr. Tonkin says that Toxoplasma actually requires a human host cell such as a neuron, to survive. Their team was able to determine how this parasite hijacks for its own growth and survival, after which it hibernates in the host cell for decades because it has already piled up food beforehand.

Toxoplasma infection leads to massive changes in the host cell to prevent immune attack and enable it to acquire a steady nutrient supply, says Dr. Tonkin. It does this by sending proteins that manipulate the host cell's machinery, thereby allowing its own growth and reproduction.


Dr. Boddey also says that some of the proteins that the Toxoplasma transmits can also influence the behavior of the host. At present, there is a high correlation between Toxoplasma infections and psychiatric disorders such as schizophrenia and bipolar disorder. Recent advances have also made it possible to check whether the proteins that the parasite sends into the host cells are able to disrupt the normal function of the nervous system which can of course contribute to the worsening of these conditions.

Once the parasite starts to infect a host, it can hibernate in the body of the host for a very long time, mostly until the host dies. For humans whose immune systems are suppressed, for example patients suffering from cancer, Toxoplasma can become active again and cause brain damage and even death.


The team of researchers have identified pathways that permit Toxoplasma to make chronic infections,
which pave the way to discovering treatments that may be able to clear the parasite.

We discovered that, similar to animals preparing for hibernation, Toxoplasma parasites stockpile large
amounts of starch when they become dormand, says Tonkin. By identifying and disabling the switch
that drives starch storage, we found that we could kill the dormant parasites, preventing from establishing
a chronic infection, he adds.

Cats are said to be the primary transmitters of the parasite. If the parasites are transmitted to pregnant
women, for example because of their contact with cat litter, there is a high risk of miscarriage of birth
defects. This means that the findings would not only be beneficial for those suffering from a chronic
Toxoplasma infection, but it could also make a vaccine that would work for people who are at risk, such
as pregnant women.

Boddey says that scientists have been wondering for a long time in how the parasite transmits its
manipulating proteins. Our study showed that the parasite includes a signature on the exported proteins
that ˜earmark' them for transport into the host cell, he said. If this transport is blocked, the parasite
becomes less dangerous. This suggests that blocking the transport would be a good way of treating
patients who are infected with Toxoplasma.