A study led by Prof. Aaron Blackwell of the Department of Anthropology at the University of California-Santa Barbara (UCSB), found that infection with helminths, a class of parasitic worms, can either positively or negatively influence a woman’s fertility.
The Tsimane women of Bolivia are known as the most fertile in the world, having an average of 10 children in their lifetimes. Some are even more fertile than the others. Researchers at the University of California at Santa Barbara collected data from over 1,000 women in this community over nine years, and made a surprising discovery about parasitic worm infections. They found that women infected with roundworm had as many as 12 children while women who had hookworm infections saw births drop to seven.
Helminth infection is prevalent in developing countries, and it is transmitted through the egg in human feces that contaminate soil due to poor sanitation. According to World Health Organization (WHO), about two billion people around the world are infected with these soil-transmitted parasites. Blackwell and his team wrote that the effects “may relate to the balance of immune responses that different worms induce. The study was carried out after one of the authors of the study, Melanie Martin – fell pregnant while investigating the study.
Researchers assessed the women for incidence of infection with the two common helminths – giant roundworm (Ascaris lumbricoides) and hookworm (Necator americanus, or Ancylostoma duodenale), to find if there was a link. It was found that 70 percent of women in Bolivia had a helminth infection. The study concluded that women infected with roundworm were more likely to become pregnant, and those infected with hookworm had a lower chance of pregnancy.
The results revealed that roundworm infection reduced the length of intervals between births, and hookworm infection increased the interval. The study predicts that women infected with hookworm are likely to have three little children, but roundworm-infected women would have two additional children. Prof. Blackwell and his team of researchers said that it is likely that roundworm and hookworm infections affect the immune system in a way that either positively or negatively impacts the chances of conception.
Blackwell told the BBC that the immune changes in a woman’s body may make it more of less friendly towards a pregnancy. Though the new findings could open up new types of treatments for those having trouble getting pregnant, women should not try to increase their chances of getting pregnant by trying to get infected with the roundworm. Infections with roundworm are common and some cases are asymptomatic — they can lead to fever, shortness of breath, anemia and can also lead to death in some cases. The study has been published in the journal Science.