LONDON (Reuters) - Italian scientists said on Friday they had found evidence of how viruses helped change the course of human evolution and said their discovery could help in the design of better drugs and vaccines.

A double helix in an undated image. REUTERS/File

They found more than 400 different mutations in 139 genes that play a role in people’s risk of catching viruses -- a finding that may also help explain why some people sail through flu season unscathed while others seem to catch every bug around.

Researchers from the Scientific Institute IRCCS, Milan University and the Politecnico di Milano analysed the genomes of 52 populations from different parts of the world with exposure to a wide range of viruses over 200,000 years of human evolution.

The researchers, whose work was published in the Public Library of Science PLoS Genetics journal, looked at places where the climate has provided friendly conditions for viruses -- such as warm, wet regions of Africa.

It is no secret that viruses have affected the human gene map -- studies have shown that 8 percent of the genome is made up of so-called endogenous retroviruses, which incorporate their genetic code into ours.

The Italian scientists searched through the genome for evidence of infection and linked it to genetic variation -- a method they thought would be a good way to find genes linked with viruses. They found more gene mutations where populations had been infected by many different viruses.

“We found that these genes had been selected -- and from this concept we can extrapolate that many of these genes might make you more or less susceptible to viruses,” Manuela Sironi, who led the work, said in a telephone interview.

Sironi stressed that the work was “very preliminary” and would need to be replicated by others and tested in the lab.

She also said a similar method to the one her team used could be used to find genes that boost or cut the risk of infections from other bugs such as bacteria.

The study is availablehere