A virus known to attack green algae in lakes and rivers can also infect human brains -- and it’s making dummies out of us. The virus, called ATCV-1, can impair cognitive activity, learning and memory, essentially making a person who has the virus less intelligent, researchers in the U.S. have found. Scientists said this is the first time the virus has been observed in people.

“This is a striking example showing that the ‘innocuous’ microorganisms we carry can affect behavior and cognition,” Robert Yolken, a virologist at Johns Hopkins Medical School in Maryland, who led the original study, told the Independent. All people have physiological differences “encoded in the set of genes each inherits from parents, yet some of these differences are fueled by the various microorganisms we harbor and the way they interact with our genes,” Yolken said.

Scientists discovered the virus accidentally while working on an unrelated study into microbes in the human throat. Throat swabs drawn from study volunteers showed unexpected traces of ATCV-1 in their DNA. Out of the 92 healthy adults screened in the study, nearly 44 percent of them had the virus, the authors said.

Study participants who had the virus performed around 10 percent worse on cognitive tests. Additionally, researchers noted the presence of the virus was correlated with lower attention spans and a “statistically significant decrease in … visual processing and visual motor speed.” While the virus is found in freshwater, there was no indication the only people who had it were swimmers and boaters. “These are agents that we carry around for a long time and that may have subtle effects on our cognition and behavior,” Yolken told Healthline. "We're really just starting to find out what some of these agents that we're carrying around might actually do.”

Subsequent tests involving mice produced similar results, Newsweek reported. Researchers inserted infected green algae into the mouths of mice and had them perform a series of lab tests. It took animals that had been injected with the virus 10 percent longer to find their way out of mazes. They also spent 20 percent less time exploring new objects than uninfected mice, researchers found.