The algae virus, never before observed in healthy people, was found to affect cognitive functions including visual processing and spatial awareness. 

Scientists at Johns Hopkins Medical School and the University of Nebraska stumbled upon the discovery when they were undertaking an unrelated study into throat microbes.

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Surprisingly, the researchers found DNA in the throats of healthy individuals that matched the DNA of a virus known to infect green algae.

Dr Robert Yolken, a virologist who led the original study, said: “This is a striking example showing that the ‘innocuous’ microorganisms we carry can affect behaviour and cognition.