New brain-altering parasite discovered

Dr Alex Ford examines an amphipod shrimp similar to the infected specimens taken from Langstone Harbour.

Dr Alex Ford examines an amphipod shrimp similar to the infected specimens taken from Langstone Harbour.

A new species of brain-altering parasite has been discovered in Hampshire by University of Portsmouth scientists.

A study led by marine biologist Dr Alex Ford found that amphipod shrimps in Langstone Harbour, Portsmouth, were infected with worm-like parasites that changed the shrimps’ behaviour to make them swim into the light, where they were more likely to be eaten by birds.

The new species – which has not yet been named – is a type of parasite that lives inside a succession of hosts before eventually being consumed by birds. The parasite’s eggs are then expelled in the birds’ faeces, allowing a whole new life cycle to begin.

The research, published in Parasitology journal, showed that a hormone, serotonin, produced during the infection made the shrimp want to swim away from darkness and towards light.

Scientists are still investigating whether the serotonin is produced by the parasite or if the parasite’s physical presence alters the shrimp’s brain chemistry.

Serotonin is one of the chemicals that controls behaviour in all animals, including humans, but the shrimp’s response – to move towards light – seems to be unique to crustaceans.

The study, funded by the Natural Environment Research Council (NERC), mapped the population of the shrimp in the harbour over 18 months, identifying the parasite as a previously unreported species.

Dr Ford, of the University’s Institute of Marine Sciences, said: “We think we know all the species that live on our doorstep, so it’s really exciting when we find a new one. I expect that shores around the UK will be harbouring other parasites that are completely unknown to science at the moment.”

According to Dr Ford, this is only the second trematode species recorded that manipulates the behaviour of its shrimp host.

The parasite’s presence was shown by the study to have a dramatic effect on the shrimp population.

The trematode parasite.

The brain-altering trematode parasite.

“When the parasite numbers go up the host numbers go down, which fits in with the idea that the parasite wants its host to be eaten, because the parasite needs to be inside a bird to complete its life cycle,” said Dr Ford.

“We did some experiments on the shrimps and gave them the choice of being in the light or dark. The ones with the parasite wanted to be in the light, whereas the ones without wanted to be in the dark.

“This is the first study to specifically measure which genes linked to serotonin have been altered by infection.”

FORD-shrimp

Shrimps were made to swim towards light after infection by trematodes parasites.

Dr Ford said: “If it turns out that the parasite is actually producing a chemical that can alter brain chemistry, that has some very interesting repercussions.

“It will help us better understand the mechanisms controlling crustacean behaviour and may even help us better understand ways to regulate serotonin in humans.”

Serotonin is widely thought to be a major contributor to feelings of happiness and well-being.

The affected shrimp species is found in waters from Iceland to Portugal, but it is not yet known whether the parasite lives alongside it in all of those places.

The latest research follows a study in 2010 led by Dr Ford in which shrimps exposed to antidepressants were shown to become more attracted to light.

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