Scimex: 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 Úbeda 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.