A study of the Tsimane people of Bolivia has shown parasites to have a marked effect on female fertility.
A husband and wife team of researchers were in Bolivia conducting a study on the Tsimane people. That was when they decided to have a baby. The wife got pregnant very quickly and she attributed this sudden spurt of fertility to parasites.
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Other experts in the field began surmising whether she might be right on this one. The study on the Tsimane began to explore whether parasites did actually have an effect on female fertility levels.
It was found that various kinds of helminths – that is parasitic intestinal worms – had both good and bad effects on female fertility. Especially the timing of the pregnancy was markedly influenced by the helminths.
While hookworm infections tended to increase the intervals between births, in younger women, who were infected by roundworm, the birth intervals were smaller than usual. The scientists examined two sorts of parasites: the hookworm and the giant roundworm.
"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," said lead author Aaron Blackwell, an assistant professor in UCSB's Department of Anthropology.
"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."
Those who had roundworm infections were likely to conceive while those with hookworm were not likely to do so. The helminths probably cause infections that affect the immune system which in turn triggers the reproductive system of the females to behave erratically.
Thus helminths have a substantial effect on population levels among the Tsimane. While helminth infections are known to cause anemia and other diseases, most of the Tsimane females who got infected showed little or no symptoms.
They often did not report any illnesses due to the infection. In fact, they were more of less oblivious of the infection. But the fact was that their immunoglobulin E was pretty high due to the parasites. What this shows is that infection by worms has a lot of repercussions ranging from health to reproductivity.
The two extra children per woman that the Tsimane have shows that they as a people consider us westerners as poverty-stricken. Most of the fertility levels of females in occidental societies have taken a nosedive. But in case of the Tsimane people, every 17 years they replenish their population levels by reproducing very rapidly.
This research on these primitive people could yield information that helps in the making of novel fertility drugs. There are so many bad things that have good effects that to start naming them is a formidable task. The soil contains many bacteria that are good for health and our ultra-modern hygiene sometimes produces problems for us like declining fertility levels among females.
"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," said co-author Michael Gurven, a UCSB anthropology professor and co-director of the Tsimane Life History and Health Project.
"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, even though the findings may be less applicable in developed populations where women only have a few children over their lifetime."
"In fact, the Tsimane look at us as poor because we only have one or two children," Gurven added. "Their population growth rate is almost 4 percent, so every 17 years or so, they double their numbers."
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The findings of this research appear on Thursday in the journal Science.