We catch viruses from animals all the time, but what about from plants? A virus previously thought to only infect algae has been found in the throats of humans, and scientists have discovered that it's been doing odd things to their brains.

An algal virus called ATCV-1 was first discovered several years ago in brain tissue samples taken from deceased humans. Because the researchers couldn't confirm if the virus had made its way there before or after death, not much came from the discovery initially. But more recently, ATCV-1 was discovered again, and this time in the throats of patients affected by psychiatric disease who were very much alive. Was there a connection between the presence of this little-known virus and the patients' psychiatric conditions? Led by paediatric infectious disease expert Robert Yolken, a team of researchers from Johns Hopkins University in the US decided to find out.

ATCV-1 virus is a type of chlorovirus, which typically infects certain species of freshwater green algae. While viruses that infect what's known as 'higher plants', such as ferns, conifers, and flowering plants, are among the smallest viruses known to science, the viruses that infect algae are some of the largest found to date. They have a whopping 600 protein-encoding genes, and act more like bacteria than a virus. They also have the ability to change the cognitive function of their human hosts, as Yolken and his team discovered. 

To do so, they first wanted to find out if the virus was present in healthy people, having already found it in psychiatric patients. Of the 92 healthy people they checked, all based in Balimore in the US, the virus was found in 43 percent of them, and it appeared to be doing weird things to their brains.

According to Elizabeth Pennisi at Science, the subjects who were infected with the virus performed 10 percent worse than their uninfected peers when asked to complete visual processing tasks. One such activity involved drawing a line that connected a sequence of numbers spread randomly across a page, and the infected patients completed it 10 percent slower. They were also shown to have shorter attention spans, and a higher probability of being distracted, the researchers reveal in their study published in Proceedings of the National Academy of Sciences. As Pennisi notes, "The effects [of ATCV-1] were modest, but significant."

Taking their research further, Yolken's team infected a number of lab mice with the ATCV-1 virus, and just like the human subjects, both infected and uninfected mice were prompted to perform a number of cognitive tests. The results from the mice ended up very closely matching the results found in humans, with the infected mice showing shorter attention spans and a worse performance in spacial and visual processing tasks. Just like the infected humans, the infected mice took 10 percent longer to navigate their way through various mazes, and spent 20 percent less time looking for objects hidden in the maze. "They had created stupid mice, it seemed, or at least mice that had a harder time with some tasks," says Michael Byrne at Motherboard.

"The similarity of our findings in mice and humans underscores the common mechanisms that many microbes use to affect cognitive function in both animals and people," one of the team, neurobiologist Mikhail Pletnikov, said in a statement

The team then studied genes in the hippocampus region of their mouse subjects' brains to see if the virus was having any effect. A functioning hippocampus is crucial for proper spacial awareness and the formation of memories. According to Pennisi at Science, the team found that the presence of the ATCV-1 virus changed the activity of almost 1,300 genes in the hippocampuses of the mice it infected. While the researchers didn't find the virus actually living in any of the mice brains, Yolken suspects that it has an influence on the body's immune system from where it sits in the throat, and this stimulates responses in the brain that cause certain genes to be switched on and off.

So in a sense, says Byrne at Motherboard, ATCV-1 could be acting like the notorious parasite Toxoplasma gondii, which makes its way from cats to humans and is possibly messing with our brains. Rather than making its hosts sick, the virus could simply be living inside them like a parasite, and its presence happens to have some notable but fairly harmless effects.

So maybe you do have an algae virus and it's making you slightly dumber than the uninfected person next to you. Just make them watch this video for 50 seconds and you'll have probably evened things out. 

Sources: Science, Motherboard