Nearly half of us could be infected with a virus which makes us more stupid, scientists have found

The startling discovery suggests that millions may be carrying a long-lasting infection which dulls the brain. Scientists found the virus living in the throats of 44% of patients tested in a small study. Those who were carrying the infection performed worse in intelligence tests, even when education and age were taken into account. The virus - called chlorovirus ATCV-1 - was previously only known to appear in green algae in freshwater lakes. The researchers, from Johns Hopkins University in Baltimore and the University of Nebraska, have not established how the virus comes to infect humans. It does not seem to have infected just swimmers or watersports fans, probably ruling out a link to algae itself. Instead it could be that humans have long carried the virus, but it had not previously been looked for by doctors. Study author Professor Robert Yolken, of Johns Hopkins medical school, said that the millions of viruses living in the human body are being investigated by experts for the first time. The research suggests that the ATCV-1 virus alters the genes in the brain. The team found the virus in throat swabs from 40 out of 92 volunteers, and discovered that those with the virus performed measurably worse in cognitive testing. They then confirmed their findings in tests on mice. Giving the virus to mice resulted in a decrease in recognition memory and other brain functions, they found. Tests showed that the virus had broken through the barrier between blood and tissue, altering the activity of genes in the brains of the mice. The genes affected including those producing dopamine - a vital hormone which influences memory, spatial awareness, emotion and pleasure.