American scientists have located a virus that attacks human DNA, which may cause those infected to be less intelligent, impairing brain activity, learning and memory.

Researchers from Johns Hopkins School of Medicine and the University of Nebraska have identified traces of an algal virus, known as ATCV-1, in throat swabs drawn from healthy volunteers which appeared to lessen their mental capacity.

The researchers had originally been working on an unrelated study into throat microbes when they unexpectedly located traces of ATCV-1 in human DNA samples. At first the research team, led by Dr Robert Yolken of Johns Hopkins, didn’t know what ATCV-1 was, and had to carry out a database search to find out more about the unknown virus.

ATCV-1 typically infects a species of green algae found in lakes and rivers, and has not previously been known to infect humans. However, when Yolken’s team screened a group of 92 healthy volunteers who were taking part in a study on cognitive function, the virus was found to be present in 43.5% of them.

According to the study, those infected with the virus performed around 10% worse on tests analysing visual processing speeds. In one test, infected volunteers were slower to draw a line connecting a sequence of numbers randomly distributed on a page than their uninfected counterparts.

The researchers found that the presence of the virus was linked to lower attention spans and decreased spatial awareness, and a “statistically significant decrease in the performance on cognitive assessments of visual processing and visual motor speed”. Researchers found no connection between slower brain function and variables such as differences in sex, education level, income, race, and even cigarette smoking.

The team carried out further tests, in which they injected uninfected and infected green algae into the mouths of mice and put them through a series of lab tests. The results revealed that infected animals took 10% longer to find their way out of mazes and spent 20% less time exploring new objects than uninfected mice, conforming to the findings amongst human volunteers. According to the study, the virus appeared to impair the “learning, memory formation, and the immune response to viral exposure” of the mice.

Professor James L. Van Etten of the University of Nebraska, who was a member of the research team, told Newsweek that little is currently known about how the virus could be transmitted to humans in such abundance, but that they had “no reason to believe that [the viruses] are contagious among people or animals”.

Van Etten said that the team has yet to identify any potential indicators of the virus’s presence in humans. “My best guess is that these viruses may infect another microorganism besides the algae that we have been studying... This other microorganism may be the way that the virus gets into the throat,” he added.