Melissa Wiese/Flickr

Scientists have figured out how a parasite transmitted by cats may alter our behaviour

Scary.

PETER DOCKRILL
10 DEC 2015
 

A common parasite often transmitted via cat litter and hosted by up to 80 percent of people poses no threat to most of us, but it can cause serious complications for pregnant women or those with compromised immune systems.

Fortunately, a new study by researchers in Australia has figured out how the parasite, Toxoplasma gondii, captures host cells and stockpiles food to keep itself alive, and the discovery could enable treatments that help us beat this uninvited guest.

 

In human infections, Toxoplasma requires a human host cell, such as a neuron, to set up house in. To enable its own growth and survival, the parasite hijacks this host cell and can then hibernate for decades by creating food reserves.

"Toxoplasma infection leads to massive changes in the host cell to prevent immune attack and enable it to acquire a steady nutrient supply," said Chris Tonkin of the Walter and Eliza Hall Institute. "The parasite achieves this by sending proteins into the host cell that manipulate the host's own cellular pathways, enabling it to grow and reproduce."

The parasite, which also infects humans through undercooked meat harbouring the pathogen, can live undetected in its hosts for the rest of their lives. Even more unsettling: the manner in which Toxoplasma manipulates its immediate environment to build up its larder may result in the behaviour of the human host being altered.

"There is a fascinating association between Toxoplasma infection and psychiatric diseases including schizophrenia and bipolar disorder," said Tonkin. "It is now possible to test whether proteins sent from the hibernating parasite into a host neuron disrupt normal brain function and contribute to development of these diseases."

With the researchers having identified the pathways that allow Toxoplasma to establish ongoing infections lasting for decades, it's possible that treatments can be developed to clear out the dormant parasite. It turns out that the key to the bug's ongoing survival isn't all that different to what some organisms do on a much more macroscopic scale.

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

The researchers' findings are published in Cell Host & Microbe and eLife. Further study will now look into whether the new discoveries can lead to vaccines to protect pregnant women, or help develop medications to clear out infections in those with weakened immune systems.

In the meantime, if you fall into either of those categories, it might be wise to steer clear of kitty litter and ensure that any meat you eat is well cooked.

"Cats are one of the primary transmitters of Toxoplasma parasites," said Tonkin. "If the parasites are transmitted to pregnant women, for example through contact with kitty litter, there is a substantial risk of miscarriage or birth defects. We hope to use our discoveries to develop a vaccine that stops cats transmitting the parasite, to prevent these potentially catastrophic consequences."

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