A research team from the University of California, Santa Barbara (UCSB) collected nine years’ worth of data from an indigenous community in Bolivia and found that parasitic worm infection could help or harm a woman’s fertility.
The study found that the presence various species of parasitic helminths in the intestines could have an impact on when the next pregnancy of a Tsimane woman would be.
"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,” explained lead study author Aaron Blackwell, an assistant professor at UCSB's anthropology department.
Examining infections with the two most prevalent parasites, hookworms and giant roundworms, the team discovered that women afflicted with the latter were more likely to be pregnant while those with the former were less likely.
The researchers estimated that hookworm-stricken females would likely mother three fewer kids than uninfected ones, while roundworm-infected women would have two additional ones.
Tsimane women give birth to nine kids on average, and their population growth rate is nearly 4 percent. This means the Tsimane population doubles in size every 17 or so years.
According to Blackwell, the opposing results were probably due to the effects of helminth infection on a person's immunity, which subsequently affects reproductive potential. Such infections, he added, may significantly affect the demographics in developing countries.
“[T]hese results may also have implications for fertility in developed populations, where many fertility problems are connected to autoimmune disorders,” he warned.
Helminth infections may lead to anemia as well as other fatal conditions, but Tsimane patients often show no symptoms and do not know of the illness.
UCSB anthropology professor Michael Gurven, a study co-author, said that while they are yet to know the exact mechanism behind the findings, they suggest that immune modulation, through worms thriving in the intestines, can greatly affect the body.
The results, though, may apply less to women in developed nations who have no or only a few children in their lifetime.
Parasite immunologist Rick Maizels from the University of Edinburgh dubbed it a “very original” research into the impact of parasitic worms on reproduction. “I think it’s going to spark a lot of other investigations,” he said.
Over a billion people worldwide, mostly in tropical areas with grave sanitation concerns, are affected by intestinal worms.
Giant roundworms, for instance, live in the small intestine and consume a part of their host’s food. Certain hookworms, too, puncture the intestinal lining and, like vampires, drink the blood of their host.
The findings of the study have been published in the November issue of Science.
Photo: Sustainable Sanitation Alliance | Flickr