We’ve often discussed helminths and their impact on human health, and researchers have recently provided more insight as to how these infective parasites can influence female reproductive health. The immune system plays an important role in fecundity in women. Shifts in immune responses in regulation are dynamic and these changes can have influence on pregnancy. Helminths are known to induce marked immunological changes and they infect 500 to 800 million people worldwide. In addition to modulating systemic immune responses, helminths are also known to directly infect reproductive organs or even the fetus. While studied extensively in animal models, there is little known as to how helminths influence reproductive processes in humans. A conglomerate group of scientists sought investigate how helminth infection could affect fecundity rates in women, hypothesizing that helminth infection during pregnancy may increase fecundity because the helminth-mediated immunologic responses may in fact modulate those that impair fertility.
The researchers collected 9 years-worth of health data from 986 Bolivian women who were forager-horticulturists residing in the Amazonian lowlands of the country. Western medicine and contraceptives are not used in this region, and it is estimated that different types of helminths infect up to 70% of the population. Cox proportional hazards model first determined that there was an association between helminth infection and birth spacing. Next, it was shown that women infected with hookworm were associated with a delayed age of first pregnancy. Interestingly, and in contrast to hookworm, roundworm infection was associated with early first births (in comparison to hookworm) and shortened interbirth intervals. The researchers postulated that these differences in associations could be explained by each respective helminth species unique effect on the immune system modulation. Specifically, roundworm infection is associated with regulatory T cell (Treg) Type 2 immune activation, while hookworm infections are associated with mixed Treg immune activation (e.g. both Type 1 and Type 2 activation). The association with the specific immune response could also explain why roundworm association was shown to be more favorable to conception, as Treg Type 2 activation more closely resembles pregnancy immune system activity while a Type1/Type2 mix more closely resembles an inflammatory response.
From a broad viewpoint, these findings are interesting as they point to a species-host interaction that may have an underlying - and underappreciated - influence on demographic/population distribution. The study of helminths is deserving of more attention, as we continue to acquire a wealth of information from their interactions with humans and implications on human health.