Search Here

After a nine-year study on the Tsimane people of Bolivia, scientists have made an amazing discovery---that parasitic worms affecting women can impact their fertility.

University of California Santa Barbara  scientists found that women infected with the giant roundworm (Ascaris lumbricoides) were more prone to becoming pregnant, while those infected with hookworm (either Necator americanus or Ancylostoma duodenale) were less likely to get pregnant.

"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 Tsimane woman's next pregnancy," lead study author Aaron Blackwell, assistant professor of anthropology, said in a press release.

While Tsimane women give birth to an average of 10 children, those with parasitic roundworms showed shorter birth intervals and gave birth to two additional children, having as many as 12 children in their lifetime. Women infected by hookworms showed longer birth intervals and had three less children compared to women who did not have either roundworm or hookworm infections, producing just seven children on average during their lives.

Hence, the effect of parasitic worms in women's fertility was attributed to "the balance of immune responses that the different worms induce, rather than to the physiological costs of parasitism."

"These opposing effects are likely due to helminth infection affecting the immune system, which in turn affects the likelihood of conception," Blackwell explained. "Our findings suggest that helminth infections may have substantial effects on demographic patterns in developing populations. Further, these results may also have implications for fertility in developed populations, where many fertility problems are connected to autoimmune disorders."

Moreover, Tsimane women infected with parasitic worms did not exhibit symptoms and had "extremely elevated" immunoglobulin E levels. Earlier studies revealed that such parasitic worms influenced the likelihood of getting related diseases.

"This study examines yet another domain where helminths and their regulatory effect on the immune system may be relevant to broader aspects of health and well-being," study co-author Michael Gurven, anthropology professor and co-director of the Tsimane Life History and Health Project, said in the press release.

The study was published in the Nov. 20 issue of the journal Science.