Man flu? Germ evolution may be to blame

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Scientists say some viruses have actually evolved to cause less-severe diseases in women than in men

Some pathogens may adapt to cause less-severe disease and lower frequency of death in women than in men, according to a study published in Nature Communications this week.

In the past researchers have assumed that sex differences in the severity of certain pathogen-borne diseases are due to stronger immune responses in women.

However the study authors argue that women are more valuable to the virus than men are, because of the way they can pass pathogens to their children during pregnancy, birth and breastfeeding.

“It has already been established that men and women react to illness differently, but evidence shows that viruses themselves have evolved to affect the sexes differently,” says Professor Vincent Jansen, from the School of Biological Sciences at Royal Holloway, University of London.

“Viruses may be evolving to be less dangerous to women, looking to preserve the female population,” adds Dr Francisco Úbeda, also from the School of Biological Sciences at Royal Holloway.

“The reason why these illnesses are less virulent in women is that the virus wants to be passed from mother to child, either through breastfeeding, or just through giving birth,” says Dr Úbeda.

“Survival of the fittest is relevant to all organisms, not just animals and humans. It’s entirely probable that this sex-specific virulent behaviour is happening to many other pathogens causing diseases. It’s an excellent example of what evolutionary analysis can do for medicine.”

Their paper used mathematical modelling to argue that natural selection favours viruses that have a lower rate of fatality in women than in men.

They specifically looked at the virus HTLV-1, which can cause leukaemia in infected individuals, in Japanese and Caribbean populations.

See the full article here.

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