Brain and Body

Women Infected With Roundworms Are More Fertile, Study Finds

November 30, 2015 | Joanne Kennell

Adult Loa Loa parasite
Photo credit: NIAID

This parasite could be used for future fertility treatments.

New medical treatments sometimes come from the most unlikely places, like antibiotics found in soil bacteria, and a painkiller developed from centipede venom. So when I tell you that being infected with a parasitic worm could be a good thing, try not to squirm.

I will admit that this was a tough one for me to write about.  Just thinking about a wriggling worm roaming around in your intestines is enough to make some people queasy.  According to doctors, approximately 60 percent of people around the world are infected with some sort of worm, but they are generally harmless and produce no symptoms.  

As it turns out, if you are a woman and are infected with a certain type of roundworm, you have a greater chance of getting pregnant.  

New research has shown that indigenous women in Bolivia have more children if they are infected with the roundworm species Ascaris lumbricoides.  A team of anthropologists from the University of California, Santa Barbara, studied 984 Bolivians, the Tsimané people, for nine years and identified a correlation between roundworm infection and fertility.  

SEE ALSO: Watch a Huge Parasite Make an Escape After Its Host Dies

Women infected with the species of roundworm had earlier first births, shortened interbirth intervals and were found to conceive, on average, two or more children than uninfected women.  The Tsimané people are often infected with roundworms and hookworms as a result of contaminated food and water, but few — if any — show symptoms.

"We found that different species of helminths — a family of parasitic intestinal worms — could have either positive or negative effects on the timing of a Tsimané woman's next pregnancy," said lead author Aaron Blackwell.  "Hookworm infection tended to increase the length of the intervals between births and that was consistent across all ages. But younger women infected with roundworm had shorter birth intervals."

Researchers found that women who were chronically infected with roundworm would have an average of two more children that those never infected, and those with hookworm would have three fewer. The average Tsimané woman will have ten children in her lifetime.

The team is not quite sure how roundworm increases fertility, however, they believe it comes down to the immune system.  In healthy women, ovulation triggers fewer type-1 T cells which attack foreign bodies and instead produces type-2 T cells which only produce antibodies.  This immune response is what allows a woman’s body to tolerate “invasive” bodies such as sperm and stops the immune system from destroying a fertilized egg before it attaches to the uterine lining.

Researchers believe that roundworms trigger this same response, while hookworms increase the production of type-1 cells.

"Although we don't know the precise mechanism behind these results, our findings are still compelling and suggest that immune modulation — via our 'old friends' the intestinal worms — can have far-reaching effects on the body," said study co-author Michael Gurven.

Although still unproven and further testing is required, the results could lead to improved fertility treatments.  

"These results may also have implications for fertility in developed populations, where many fertility problems are connected to autoimmune disorders," said Blackwell.

Using parasites to treat ailments is not a new science.  Parasitic helminths have been used in patients with inflammatory bowel conditions, asthma, and Crohn's disease as they alter and suppress immune responses.  But heavy infections of the parasites can lead to blood and protein loss, abdominal pain, physical and cognitive growth issues, intestinal blocking and stunted growth in children.

“Whilst I wouldn’t want to suggest that women try and become infected with roundworms as a way of increasing their fertility,” said co-author Allan Pacey, “Further studies of the immunology of women who do have the parasite could ultimately lead to new and novel fertility enhancing drugs.”

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