In a very strange association, women who are infected with parasitic worms can experience either an increase or decrease in fertility, depending on which worm has invaded the intestine.
A group of researchers including Prof Aaron Blackwell of the University of California in Santa Barbara studied a tribe in Bolivia called Tsimane. This group is special in terms of reproduction and family since the average household has nine children, which is significantly higher than the one child per family average in Canada or 1.92 in the UK.
When the researchers studied more than 900 of these women for a period of nine years, they discovered that around 70% of them are infected with a certain species of roundworm called Ascaris lumbricoides. The infection, further, isn't sudden but lasts throughout the women's lifetime. The presence of the parasite therefore is associated with increased fertility by adding two more children in the family.
The childbirth outcomes, however, were different when they looked into women who had hookworms gave birth for a fewer children. About 50% of women between the ages of 26 and 28, which still belong to the childbearing years, are struggling to get pregnant.
The researchers hypothesized that the worms may change the way the immune system works, which then increases or decreases the likelihood of pregnancy. In previous two studies, it's been discovered that the immunity also adjusts itself as part of the body's preparation for conception.
In the case of women with the roundworms, for example, the parasite may decrease immune response as a way of protecting the fetus that may be viewed by the immune system as a potential threat.
The research, however, doesn't establish the cause between fertility and infection but only a possible link. Further, while the study may be a consideration in creating novel fertility drugs, the researchers are not advocating infection.
The results of the study are now published in Science.
