Men are more vulnerable to certain diseases than women. The pathogens that are more deadly in the less-fair sex include one that causes tuberculosis, as well as the viruses that can ultimately lead to tonsil cancer (namely the HPV virus) and Hodgkin's lymphoma (Epstein-Barr virus). In a new study, scientists have shown for the first time that this might not be blamed on weaker immune systems in men, but rather on the fact that viruses actually take it easier on women.

In a mathematical model of virus transmission, study authors Francisco Ubeda and Vincent Jansen at the Royal Holloway University of London dialed up the virulence for a pathogen in men, while dialing those numbers down in women. They found that the model could accurately explain why Japanese men are as much as 350 percent more likely to develop a type of fatal, virus-induced leukemia compared to women. At the same time, the model also explained why that same virus is equally fatal to both men and women in the Caribbean.

As it turns out, Japanese mothers tend to breastfeed their babies longer than Caribbean women, which gives the virus more opportunities to pass from mother to child. Over the years, the researchers suggest, the virus might evolve to be less harmful to the female host, so it could linger longer and improve its odds for passing on to more victims. After all, a virus's goal isn't actually to kill you—it only wants to keep reproducing itself as much as possible.

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The researchers point out that their conclusions call into question the prevailing wisdom about sex differences in our immune responses. Until now, scientists believed that certain viruses were more harmful to men because male sex hormones somehow interfered with the immune system. (Meanwhile, non-scientists believed men were just babies about their symptoms.) The study authors point out that if this was actually happening, you'd see that weaker immune response only after your hormones kicked into high gear during puberty, which has not been observed.

Although the mathematical model seems to work, scientists will still need to figure out how, exactly, a virus figures out whether it's infecting a man or woman, and also how it then manages to be more cruel to men than women. You might remember from high school biology that a virus is little more than a strand of DNA or RNA, hardly enough to be called "alive," and doesn't have any capacity for strategy or decision making.

That opens the door for future treatments that could trick the virus into thinking it's in a female host, triggering its less-harmful mode. "It may be possible to switch on the phenotype for women's virulence in pathogens infecting men, thus reducing the mortality they induce," the researchers write. Spoofing gender to viruses could give men a fighting chance against potentially lethal infections.