I recently read this article on the BBC News website and was quite surprised to find that parasites can be good for women. There is evidence from a nine-year study that women infected with roundworm (Ascaris lumbricoides) would have 2 more children over a lifetime than uninfected women. This seems to be the case in the Bolivian Amazon, where women have 9 children on average and 70% of the population are infected by parasitic worms. However, it was also found that hookworms had the opposite effect and often lead to 3 fewer children in a lifetime.
So far, we don’t know what is causing this but it could be due to the changes in women’s immune systems caused by these worms. Hookworms cause both type 1 T cells and type 2 T cells to be produced whereas roundworms tend to make the immune system produce more type 2 T cells, which make embryos more likely to survive. Type 1 T cells tell other cells to directly attack pathogens whereas type 2 T cells tell cells to produce antibodies. Hookworms could also cause anaemia, which then leads to infertility.
These findings could lead to drugs that can be used to increase women’s fertility in the future but there is a lot more work that has to be done before these roundworms can be used for women with fertility problems.