Parasite helps mice lose fear of cats – and get eaten

We often forget that fear is a survival instict. That is, until we get injured or killed by something we should have feared.

A new study out of the University of California-Berkeley has found an unlikely way to switch off fear (in mice).

They found that a protozoan parasite Toxoplasma, which can be deadly to humans, helps mice lose their fear of cats – permanently. Not a good thing for mice that shrug off a hungry cat.

Scientists are fascinated by the long-lasting effects of the parasite.

“Even when the parasite is cleared and it’s no longer in the brains of the animals, some kind of permanent long-term behavior change has occurred, even though we don’t know what the actual mechanism is,” graduate student Wendy Ingram, said in a statement.

After injecting the mice with the parasite, the researchers monitored their effects until the mice had fully recovered.

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During and after the experiment, they tested the mice's reaction to bobcat and rabbit urine – the latter usually prompting no reaction in mice.

The mice had no fear of either while infected and post-infection.

Despite the parasite being cleared out of their system, the loss of fear remained.

The results are important given that about one third of the world has been infected by the parasite, which has been linked to depression and schizophrenia in people.

For those who are immune compromised, the infection can be fatal.

The results offer more insight into the common parasite and its incredible ability to alter brain chemistry.

The findings were published in the journal PLOS ONE.