Humans and our parasites have evolved together over the millennia in some strange, mutually beneficial ways. For instance, scientists have identified some intestinal parasites that can boost your immune system or reduce inflammation in the body.
Now a new unexpected benefit has been discovered, but this one might be a little hard to stomach. It turns out that women who are infected with giant roundworm (Ascaris lumbricoides) have an easier time getting pregnant, reports NPR.
Giant roundworm is the largest and most common parasitic worm in humans. They can grow to over a foot in length inside your intestine, and one billion people are estimated to be infected worldwide. Though squirm-inducing to think about, giant roundworms actually live rather peacefully within your gut, usually causing only minor abdominal discomfort or no symptoms at all. Eggs of A. lumbricoides have been identified in archeological coprolites more than 24,000 years old, so these parasites have been with us for a long time.
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On a hunch, anthropologist Melanie Martin, who was an author on the roundworm study, wondered if being infected with parasites might be beneficial to a woman's ability to conceive. Her reasoning went like this: A human fetus is actually a lot like a parasitic worm. (Bear with us here.) Or rather, both the fetus and worm represent foreign bodies that a woman's immune system wants to attack. In fact, women's bodies probably spontaneously abort most pregnancies.
So, Martin wondered, if a woman's immune system is already dampened due to a worm infection, maybe that will make her less likely to reject a fetus.
It turns out, she was right. A group of anthropologists collected data on about 1,000 women living in the Bolivian Amazon, where roundworm infection is prevalent. They found that women infected with the parasite had shorter intervals between births, started giving birth at an earlier age, and had two children more on average than women who were never infected.
It's a remarkable finding, but researchers do preach caution. While the study established a correlation between roundworm infection and fertility, it has not yet confirmed a cause. It's still possible that some other related factor could be affecting female fertility.
Another reason for caution is that not all parasitic worms are created equal. The study also looked at women infected with another intestinal parasite, the hookworm, and found that these women actually experienced the opposite effect as those infected with roundworms — their ability to conceive decreased.
So, to put it mildly, researchers do not recommend that women struggling to get pregnant rush out and get themselves infected by roundworm. (Because eww.)
"No. I would definitely not recommend women who want to conceive run out and stomp through latrines and swallow a bunch of dirty water," said Martin.
Martin and colleagues are already planning a follow-up investigation to better measure exactly how these parasites might benefit or harm us. They hope this research can garner a better understanding of the weird relationship humans have with their parasites, and also how our health might be affected negatively or positively when we become parasite-free.