Some intestinal parasites affect Tsimane women fertility according to a newly published study featuring in the journal Science.
Everything started with an antrhopologist’s fieldwork in Bolivia, studying the Tsimane population dwelling in the Amazonian forest. Dwelling in the central lowlands of Bolivia the Tsimane population fertility and birth rate is quite high. On average, Tsimane women have nine children. To understand what underpins this fertility Aaron Blackwell, assistant professor with the Department of Anthropology of the University of California at Santa Barbara and her team conducted an analysis of longitudinal data spanning nine years of research.
What they found was surprising: some intestinal parasites affect Tsimane women fertility. The parasites, intestinal worms belonging to the helminths family affect the timing of the women’s pregnancies.
According to Blackwell, the study conclusively showed that Tsimane women infected with hookworms had longer birth intervals despite the age spectrum. Tsimane women infected with roundworm had shorter birth intervals. The latter results were consistent for young women.
These two intestinal worms are the most common. The hookworm or Necator americanus as well as the giant roundworm or Ascaris lumbricoides are found to positively or negatively affect birth intervals and fertility for the first time.
As the case of the Tsimane women shows, women infected with roundworm had higher chances of becoming pregnant. In addition, they were also found to have two more children than women who weren’t infected with any of the worms.
Women infected with the hookworm had fewer chances to become pregnant. At the same time, they had three fewer children than the Tsimane women who weren’t infected with any of the intestinal worms. The reproductive lifespan in light of these findings thus mirrored the fertility rates.
According to Blackwell,
“These opposing effects are likely due to helminth infection affecting the immune system, which in turn affects the likelihood of conception. Our findings suggest that helminth infections may have substantial effects on demographic patterns in developing populations”.
However, the same findings could hold some intriguing clues to fertility rates in developed nations who suffer from autoimmune disorders. With the Tsimane women, the intestinal parasites infection was largely asymptomatic. Typically, helminth infections are associated frequently with anemia and other morbidity causes.
For the Tsimane population, intestinal worm infection is not as problematic. Furthermore, the high fertility rates lead to a population growth of approximately 4 percent per year.
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