Zombie rats: Parasite lures rodents to their death by making them sexually attracted to the smell of cats



Toxoplasma-infected rats exposed to cat urine suffered an increased sexual attraction

A parasite that turns rats into zombies and manipulates them into losing their fear of cats has been uncovered by scientists.

Cat urine normally acts as natural deterrent to rodents, who are keen to keep their distance from their natural predators.

But researchers found that Toxoplasma-infected male rats exposed to cat urine suffered an increased activation in the brain regions involved in sexual attraction.

At the same time, the brain regions that govern fear were paralysed, as expected.

Danger zone: A parasite that turns rats into zombies and manipulates them into losing their fear of cats has been uncovered by scientists

Co-study author Robert Sapolsky, a professor of neuroscience at Stanford University, said: 'Normally, we would expect Toxoplasma to knock out the normal fear function in the brain, but in these rats the parasite also tapped into the sexual arousal pathway, which is strange.'

Toxoplasma requires the cat digestive system for sexual reproduction.

By not only reducing a rat's fear of the smell around cats, but also attracting them to it, the parasite makes the rodent far more susceptible to being killed by a cat.

This therefore enables the completion of the parasite's life cycle.

Toxoplasma is manipulating the fear response specifically to the urine of cats - infected rats behave normally on anxiety, fear, social and memory tasks, and retain fear behaviour to non-feline predator odours.

Co-lead researcher Patrick House, a doctoral student at Stanford University, said: 'These findings support the idea that in the rat, Toxoplasma is shifting the emotional salience of the detection of the cat.

'They also suggest that fear and attraction might lie on the same spectrum, or at least that the emotional processing of fear and attraction are not entirely unrelated.'

The scientists believe their findings may help explain the biological bases of innate fear and sexual attraction.

'The findings suggest that fear and attraction might lie on the same spectrum'

The study does not advance evidence for how Toxoplasma is altering the brain, only evidence that it does.

Previous research showed that Toxoplasma invades the brain of the host and settles near the amygdala, a region involved in a wide range of fear and emotional behaviours.

But the Stanford study extends these findings by showing that not only is Toxoplasma found in the amygdala of infected male rat hosts, but it also changes the way certain subregions of the amygdala respond to cat odour - specifically, by increasing neural activity in the presence of cat odour in regions normally activated by exposure to a female rat.

Up to a third of humans test positive for Toxoplasma, due largely to the consumption of undercooked meat or contact with cat litter.

In humans, Toxoplasma exposure is most dangerous to developing fetuses and pregnant women.

However, many recent studies find Toxoplasma exposure linked with schizophrenia, a disease noted for amygdala dysfunction and improper emotional response, compelling further investigation into what exactly Toxoplasma is doing in the host brain.