It's the stuff of horror movies: a parasite brainwashes its victim, ultimately forcing it to kill itself, so it can reproduce.

But this macabre manipulation isn't just science fiction; indeed, scientists have been aware for decades of how certain clever parasites can change the behaviour of their much larger hosts.

Malaria parasites, for example, can make mosquitoes more attracted to humans, increasing the chance of transmission.

In other instances, parasites use a bio-chemical effect called "toxoplasma" to make rats less afraid of cats, increasing their chance of being eaten and thus enabling the parasites to move to the cat, where they can reproduce.


There have even been some suggestions that toxoplasmosis can affect humans, causing us to behave in riskier ways.

"It's always a danger for us to assume that, from a biological point of view, we are the most sophisticated thing on the planet," Otago University geneticist Professor Neil Gemmell said.

"These parasites are highly specialised and have evolved a fascinating array of approaches to manipulate their hosts."

In a new study, supported with an $830,000 Marsden Fund grant, Gemmell and his team will focus on something yet more extraordinary: the potential of DNA-based brainwashing.

Two specific parasitic worms they'll investigate, found in New Zealand, are known to hijack hosts' central nervous systems, forcing them to seek water for the worm to reproduce in.

Once water is found, the adult worm explodes out of the host, killing it.

Although the mechanisms behind such amazing abilities are not well understood, one possibility is through alteration of the host's DNA.

Professor Neil Gemmell. Photo / Supplied
Professor Neil Gemmell. Photo / Supplied

"There's really two different ways the parasites could do this; it either could make something that mimics or interacts with a substance in the host that's responsible for some form of neurological decision-making, or it produces something that changes the pattern of expression of the genes responsible for the production of that substance, perhaps turning them on or off.


"It could even be a combination of the two and might not be a simple trigger, but one that elicits a number of different changes; this is what we hope to tease out."

His Otago-based team will use cutting-edge molecular and bioinformatics tools to study two distantly related parasitic worms and their hosts - one affecting cave weta, the other affecting earwigs.

They'll attempt to discover the trigger and genetic cascade through which these parasites elicit this behaviour.

"This study is unique to New Zealand, and one of the things that's really cool about it is that these parasites and their hosts are relatively common.

"For example the earwigs, together with their mind-controlling parasites are likely well established in the roses in your back garden."

Gemmell suspected that the general process was widespread among many parasite species and hosts, and that those we're aware of today could be just the tip of the iceberg.

"Host manipulation by parasites has now been documented a few hundred times spanning all major groups of animals, so probably this sort of manipulation is relatively common."

Although the project will look at parasites that affect insects, the findings will be broadly relevant to many other parasite systems, including those that affect humans and livestock.

The first seconds of life, under the microscope

Another Marsden Fund study will gain new insights into the very beginnings of life.

Researchers from Auckland University and Otago University will use cutting-edge genomic techniques to study how a zygote - the cell that forms from the union of sperm and egg - activates its newly minted genome and becomes the master of its own genetic destiny.

Study co-leader Associate Professor Julia Horsfield, of Otago University, said that when a zygote forms, its genome is kept mostly inactive at first.

"However, at a defined time-point, the zygotic genome becomes active and is transcribed - its genes are switched on," she said.

"At this crucial time, the embryo becomes master of its own destiny."

Associate Professor Julia Horsfield. Photo / Supplied
Associate Professor Julia Horsfield. Photo / Supplied

Working alongside Auckland University's Dr Justin O'Sullivan, Horsfield will test the theory that a special 3D structure forms in the cell's nucleus and permits transcription to occur and triggers genome activation.

The team will use sophisticated genomics techniques that can probe nuclear structures in zebrafish embryos.

During the study, they'll observe live imaging of the embryos and individual cells as they undergo genome activation to look at visible changes in the nucleus as genes are switched on.

"As well as aiming to discover the nuclear structure that triggers genome activation, we hope to disrupt the structure to determine how important it is for gene activation," O'Sullivan said.

Establishing how the zygotic genome was at first held inactive, and how it rapidly became activated, would provide new insights into the earliest stages of life, he said.

The $810,000 in Marsden Fund grant would also enable a new collaboration with the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden, Germany.

"It will bring our farflung team together to tackle one of the biggest enigmas in biology - how an individual expresses its genetic identity for the first time," Horsfield said.