Research press release


Nature Communications

Evolution: Pathogens sometimes go easier on women than men


特定の病原体感染症の重症度に性差が見られるのは、男性より女性の免疫応答の方が強いからだと研究者は考えてきた。これに対して、今回のFrancisco UbedaとVincent Jansenの論文には、別の説明が示されている。つまり、男性より女性における伝播経路が多い病原体にとっては、感染した女性の症状を軽くするように進化することが有効な進化戦略だというのだ。Ubedaたちは、この新知見によって、ヒト T リンパ球向性ウイルス 1(HTLV-1)感染症から成人T細胞白血病(ATL、血液がんの一種)への進行の性差が集団によって異なっていることを説明できる可能性があると考えている。例えば、カリブ海地域ではHTLV-1感染症からATLへの進行頻度に性差は見られなかったが、日本では男性の進行頻度の方が高かった。日本は、カリブ海地域と比べて、赤ん坊を母乳で育てる女性の割合が高く、授乳期間もカリブ海地域より長い。


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. Women can pass pathogens to their children during pregnancy, birth and breastfeeding, in addition to passing them to other individuals in the population the same way as men do. The research shows that the additional opportunities of transmission provided by women compared to men can exert sufficient evolutionary pressure on pathogens to drive the evolution of sex-specific virulence.

Researchers have assumed that differences in the severity of certain pathogen-borne diseases in men and women are due to stronger immune responses in women. Francisco Ubeda and Vincent Jansen provide an alternative explanation by showing that when pathogens can spread through additional transmission paths from women compared to men, adapting to cause less-severe disease in women is a successful evolutionary strategy for pathogens. The authors argue that their findings may explain variations in the progression of human T-lymphotropic virus 1 (HTLV-1) infection to adult T-cell leukaemia (ATL, a type of blood cancer) in men and women in different populations. For example, there is no difference in the frequency of progression of HTLV-1 infection to ATL between the two sexes in the Caribbean. However, progression of HTLV-1 infection to ATL is more frequent in men than women in Japan, where a higher proportion of mothers breastfeed their children, and do so for a more extended period, compared to women in the Caribbean.

The authors suggest that it makes evolutionary sense for the pathogen to cause less-severe disease in females if they provide more opportunities for transmission than males, making them a more-valuable host.

doi: 10.1038/ncomms13849

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