Scientists at the Johns Hopkins Medical School and the University of Nebraska have discovered an algae virus that makes us more stupid by infecting our brains.
The researchers were conducting a completely unrelated study into throat microbes when they realised that DNA in the throats of healthy people matched the DNA of a chlorovirus virus known as ATCV-1.
ATCV-1 is a virus that infects the green algae found in freshwater lakes and ponds. It had previously been thought to be non-infectious to humans, but the scientists found that it actually affects cognitive functions in the brain by shortening attention span and causing a decrease in spatial awareness.
For the first time ever, the researchers proved that microorganisms have the ability to trigger delicate physiological changes to the human body, without launching a full-blown attack on the human immune system.
However, the scientists do not yet know how ATCV-1 infects a human host and it's not as simple as just going swimming in a lake or pond, so there's no need to stop doing that yet.
Both humans and mice susceptible to virus
The study, entitled "Chlorovirus ATCV-1 is part of the human oropharyngeal virome and is associated with changes in cognitive functions in humans and mice" is published in the Proceedings of the National Academy of Sciences (PNAS) journal.
The researchers analysed the throats of 92 healthy study participants and discovered the presence of ATCV-1 in 44% of them.
When they conducted tests designed to measure the brain's accuracy and speed in visual processing, as well as tests measuring attention span, the participants that tested positive for ATCV-1 achieved an average of 7-9 points lower on the tests than the participants who did not have the virus in their throats.
The researchers then studied how ATCV-1 affected mice by injecting the virus into their digestive tracts.
They then put the mice into a maze, where the animals infected by the virus had a more difficult time finding their way round and were less likely to pay attention to a new object or notice a new entry that had been previously inaccessible.
ATCV-1 was able to get into the hippocampus pathways of the mice and alter the expression of genes relating to memory formation, learning and synaptic plasticity (an important foundation of learning and memory), as well as how the immune systems of the mice responded to being exposed to the virus.
A different way to look at infectious agents
"This is a striking example showing that the 'innocuous' microorganisms we carry can affect behaviour and cognition," said lead investigator Dr Robert Yolken, a virologist and pediatric infectious disease specialist at the Johns Hopkins Children's Center and director of the Stanley Neurovirology Laboratory at Johns Hopkins.
"Many physiological differences between person A and person B are encoded in the set of genes each inherits from parents, yet some of these differences are fuelled by the various microorganisms we harbour and the way they interact with our genes."
The researchers' findings are a clear example that microorganisms have a greater influence on the human body than previously released, and further research into altering microbiomes, i.e. the balance of viruses and bacteria in the body, could one day help doctors to improve people's cognition skills.
"We're really just starting to find out what some of these agents that we're carrying around might actually do," Yolken told Healthline.
"It's the beginning, I think, of another way of looking at infectious agents — not agents that come in and do a lot of damage and then leave, like Ebola virus or influenza virus."