© Walter and Eliza Hall InstituteElectron microscope image visualising the Toxoplasma parasite modifying its host's cells. Toxoplasma parasites are purple, human cells are red. The modified cells are green.
The finding could lead to a vaccine that would prevent pregnant women being infected by the Toxoplasma gondii parasite, which can increase the risk of miscarriage or severe birth defects.
And it could have implications in the treatment of mental illnesses such as bipolar and lead to drug therapies for those with compromised immune systems such as HIV and cancer patients.
In a paper published in the journal Cell Host & Microbe and in eLife, the predominantly Melbourne-based research team details how the parasite stockpiles food, giving it an energy source that it can draw on for decades.
The study also reveals a potential mechanism the parasite may use to change brain cells that may contribute to mental illness.
Lead author Dr Chris Tonkin, from the Walter and Eliza Hall Institute of Medical Research, said Toxoplasma was a common parasite that was transmitted by cats and also found in raw or undercooked meat.
Once in humans, the parasite hijacks cells in the brain, heart, lungs and muscles.
Hunting down a hijacker
Dr Tonkin said it was estimated about 35 per cent of the Australian population carried the parasite, which could remain dormant for a person's lifetime without their knowledge.
However in people with suppressed immune systems such as cancer patients it can be reactivated and lead to neurological damage or death.
In a process similar to animals preparing for hibernation, Toxoplasma parasites stockpiled large amounts of starch when they became dormant and evade the body's immune system.
But now the team have found the regulatory switch — CDPK2 — that controlled that starch storage.
"If you remove that switch the parasite can no longer control the amount of starch it stores," Dr Tonkin said. "It hyper-accumulates starch and literally blows itself up, it explodes."
He said it was hoped the discovery could lead to a vaccine that stopped cats transmitting the parasite to humans.
Could Toxo play a role in mental illness?
He said the study also revealed the Toxoplasma "modified" the host cell by sending in proteins to manipulate the host cell's function so the parasite could reproduce and grow.
There was some evidence that in brain cells these modifications could lead to personality or behavioural changes, he said.
Dr Tonkin pointed to previous studies that showed when mice were infected with the parasite they adopted behaviours that made them more vulnerable to attack.
This included making them attracted to cat urine and more likely to roam in open spaces, where they were more likely to be caught.
"If it is doing that to mice, what is it doing to humans?" Dr Tonkin said.
He said this had renewed interest in whether the pathogen may play a role in mental illness.
"No-one is suggesting it is causing bipolar disorder or schizophrenia, but maybe it is contributing," he said.
Dr Tonkin said the team had found the pathway by which proteins were transported into the host cell.
"The implication is we can use this to see if the proteins sent by the parasite are changing the behaviour of the host neuron and ultimately playing a role in the development of these diseases."
He said there was potential to block this transport system.
"If you remove it the parasite can no longer survive."
"If it is doing that to mice, what is it doing to humans?" Dr Tonkin said.
Well, there are better populations than Australians to check it out (35%? Paltry amount). Around 90% of French carry that nasty critter, or so they sat. This is enough for changing behavioural patterns of whole nations, not just causing mental illness of individuals. But somehow I doubt the scientific research in this area would be financed, at least not by government funds.