Throughout history, men have been ridiculed for their apparent inability to handle simple viruses like the common cold – otherwise referred to as the “man flu” in these cases.
But as it turns out, there may be some truth to the man flu label as researchers find that certain viruses may present themselves more virulently in men than in women.
And it may have to do with evolution.
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“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,” Vincent Jansen, professor at the School of Biological Sciences at Royal Holloway University of London, and co-author of the study, said in a statement.
Researchers looked at HTLV-1, a virus known to cause leukemia in infected people.
Infected women tend to develop leukemia less often than men, who are more likely to die from the disease.
By using mathematical modelling, researchers set out to show that natural selection favours viruses that have a lower rate of death in women than in men, especially if the virus can be passed from person to person and from mother to child.
Researchers used population samples from Japan and the Caribbean.
They found that Japanese men infected with the HTLV-1 virus were two to 3.5 times more likely to develop leukemia than women. However, the likelihood of the virus progressing to leukemia was about equal in men and women in the Caribbean.
Scientists believe the virus has become less fatal in women because the HTLV-1 virus can be passed through breastfeeding, a practice that is more prolonged in Japan.
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Researchers concluded that women were proven to be more valuable hosts for pathogens because they are able to pass them on in more ways than men can.
“Pathogens are adapting to be less virulent in women to increase their chances of being passed on to the next generation during pregnancy, birth and infancy,” says Dr. Francisco Ubeda of Royal Holloway. “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.”
A previous study by Standford University School of Medicine in 2013 found that men and women also have different reactions to flu vaccinations.
Standford researchers found women had a stronger antibody response than men, which gave women better protection against the flu.
This, they say, was more apparent in men with higher testosterone levels which scientists believe weakens a man’s immune system.
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